Method and a system for manufacturing a composite product and a composite product

ABSTRACT

The invention relates to a method for manufacturing a composite product comprising organic natural fiber material and matrix material, wherein the method comprises mixing the organic natural fiber material with the matrix material in a primary mixing stage to form a mixture. The primary mixing stage comprises a contacting step in which the organic natural fiber material comes in contact with the matrix material that is at least partly in a form of melt, and compression ratio of the organic natural fiber material is less than 8. The method further comprises forming a composite product comprising the mixture. Further, the invention relates to a composite product, a use of the composite product, and a system for manufacturing a composite product.

FIELD OF THE INVENTION

The invention relates to a method and a system for manufacturing acomposite product. Further, the invention relates to a composite productand a use of the composite product.

BACKGROUND OF THE INVENTION

Known from prior art are different wood-polymer composites which areformed from wood-based material and polymers typically by extrusion.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a new composite product. Thecomposite product may be a final product or an intermediate product.Another object of the invention is to disclose a new method and a systemfor manufacturing a composite product. Another object of the inventionis to disclose a novel use of the composite product.

The method for manufacturing a composite product according to thepresent invention is characterized by what is presented in claim 1. Thecomposite product according to the present invention is characterized bywhat is presented in claims 17 and 21. The system for manufacturing acomposite product is characterized by what is presented in claim 26. Theuse of the composite product according to the present invention ischaracterized by what is presented in claim 25.

Advantageously, the method for manufacturing a composite productcomprising organic natural fiber material and matrix material comprisesthe following steps:

-   -   mixing the organic natural fiber material with the matrix        material in a primary mixing stage to form a mixture, the        primary mixing stage comprising a contacting step, in which        -   the organic natural fiber material comes in contact with the            matrix material that is at least partly in a form of melt,            and        -   bulk density of the organic natural fiber material is less            than 500 kg/m³,            and    -   forming the composite product comprising the mixture.

Advantageously, the organic natural fiber material is crushed before thecontacting step to form bulky organic natural fiber material.

Advantageously, the bulk density of the organic natural fiber materialis less than 160 kg/m³.

Advantageously, the organic natural fiber material is mixed without aheavy compression with the matrix material in the contacting step of theprimary mixing stage, i.e. the pressure compressing the organic naturalfiber material in the contacting step is less than 2 bars, morepreferably less than 1 bar.

Advantageously, the materials are mixed in a vacuum or in a presence ofnitrogen, air and/or helium.

Advantageously, moisture content of the organic natural fiber materialis below 7%, preferably below 5% in the contacting step of the mixing.

Advantageously, at least one mixer that is capable of heating themixture is used in the primary mixing stage.

Advantageously, the content of the organic natural fiber material is atleast 10 dry wt. %, more preferably between 20 and 80 dry wt. %calculated from the total dry weight of the composite product.

Advantageously, the lignin content of the organic natural fiber materialis under 15 wt. %.

Advantageously, the amount of flake-form fiber material is at least 30dry wt. % calculated from the total amount of the organic natural fibermaterial.

Advantageously, melting point of the matrix material is under 250° C.and/or glass transition temperature of the matrix material is under 250°C.

Advantageously, the composite product is formed by injection moulding,and/or extrusion.

Advantageously, the matrix material is thermoplastic.

Advantageously, at least 90 wt. % of the organic natural fiber materialis wood material.

Advantageously, the length of at least 90 wt. % of the organic naturalfiber material is between 0.1 mm and 3 mm.

Advantageously, the composite product according to the present inventioncomprises organic natural fiber material and thermoplastic matrixmaterial, and

-   -   the amount of the organic natural fiber material is between 10        and 80 wt. % calculated from the total weight of the composite        product,    -   the amount of the matrix material is between 5 and 95 wt.%        calculated from the total weight of the composite product, and    -   density of the composite product is between 0.9 and 1.60 g/cm³        and/or density of the composite product is at least 85% of the        theoretical density

In an embodiment, the composite product is a final product. In anotherembodiment, the composite product is an intermediate product.

In an embodiment, the composite product is in form of granulates andweight of 100 granulates is between 2.0 and 4.0 g with a standarddeviation under 15%, more preferably under 7%.

Advantageously, the composite product that is dry absorbs moisture under1.5% from the weight of the composite product in the time of 48 hours(65%) RH and 27° C. atmosphere).

Advantageously, a system for manufacturing a composite productcomprising an organic natural fiber material and a matrix materialcomprises

-   -   a first mixer to mix the organic natural fiber material with the        matrix material in a primary mixing stage to form a mixture. The        primary mixing stage comprises a contacting step, in which        -   the organic natural fiber material comes in contact with the            matrix material that is at least partly in a form of melt,            and        -   a bulk density of the organic natural fiber material is less            than 500 kg/m³.

Preferably the system further comprises means for forming the compositeproduct comprising the mixture. The means for forming the compositeproduct may be included in the first mixer, or they may be a separateapparatus.

Thanks to the present invention, at least some of the followingtechnical effects may be achieved

-   -   Wetting of the organic natural fiber material with the matrix        material can be secured during the primary mixing stage.        Therefore, the organic natural fiber material can be spread        evenly among the matrix material and the fibers of the organic        natural fiber material can be wetted evenly with the matrix        material.    -   Forming of covalent or strong physical bonds or strong        mechanical attachment can be prevented between fibers of the        organic natural fiber material during the primary mixing stage.    -   Adhesion of the fibers of the organic natural fiber material to        the matrix material can be secured.    -   The composite product can be achieved without fiber        agglomerates.    -   Light color can be achieved.    -   Dispersion of the composite product can be good.    -   Particle size distribution of the raw materials of the        composition product can be controlled.    -   In an embodiment, raw materials used are lignin free.

DESCRIPTION OF THE DRAWINGS

The accompanying figures, which are included to provide a furtherunderstanding of the invention and constitute a part of thisspecification, illustrate some embodiments of the invention and togetherwith the description help to explain the principles of the invention.

FIGS. 1 to 6 show reduced flow chart illustrations of embodiments of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

In the following disclosure, all percentages are by dry weight, if notindicated otherwise.

The following reference numbers are used in this application: organicnatural fiber material,

-   11 a bulky organic natural fiber material,-   12 matrix material,-   15 mixture comprising organic natural fiber material and matrix    material,-   20 pre-treatment stage(s),-   20 pre-mixing stage,-   21 a pre-mixing step of the organic natural fiber material,-   21 b pre-mixing step of the unmelted matrix material and the organic    natural fiber material,-   23 pre-crushing stage, crushing,-   24 pre-separation stage,-   25 chemical treatment,-   27 pre-mixing apparatus,-   28 crusher, crushing device,-   29 separator,-   30 primary treatment stage(s),-   36 primary mixing stage,-   36 a contacting step of the primary mixing stage,-   36 b mixing step of the primary mixing stage,-   37 means for the primary treatment stage(s),-   38 apparatus for the primary mixing,-   39 means for forming a composite product, for example an extruder,-   39 a first step for forming a composite product,-   39 b second step for forming a composite product,-   40 composite product,-   40 a intermediate composite product, and-   40 b final composite product.

In an embodiment of the present invention, a composite productcomprising organic natural fiber material 11, 11 a and matrix material12 is formed. Advantageously, the organic natural fiber material hasbeen dried and then crushed by a grinding device 28, after which theorganic natural fiber material 11 a is mixed with at least partly meltedmatrix material 12, preferably without compression, to form mixture 15.Advantageously, the matrix material is melted in a phase in which theorganic natural fiber material adheres to the melt matrix material and,hence, the organic natural fiber material becomes wet by the matrixmaterial.

In this application, the terms “pressure compressing” and “compressing”mean pressure that is above a gas pressure of the ambient gas and hencecompresses a material. For example, in the case of the organic naturalfiber material, the pressure compressing the organic natural fibermaterial means pressure that compresses the organic natural fibermaterial and, therefore, may increase the bulk density of the organicnatural fiber material.

The term “organic natural fiber material 11, 11 a” refers to particlesthat contain cellulose. In other words, the organic natural fibermaterial can originate from any plant material that contains cellulose,i.e. both wood material and non-wood material can be used.

The wood material can be softwood trees, such as spruce, pine, fir,larch, douglas-fir or hemlock, or hardwood trees, such as birch, aspen,poplar, alder, eucalyptus, or acacia, or a mixture of softwoods andhardwoods. Non-wood material can be agricultural residues, grasses orother plant substances such as straw, coconut, leaves, bark, seeds,hulls, flowers, vegetables or fruits from cotton, corn, wheat, oat, rye,barley, rice, flax, hemp, manila hemp, sisal hemp, jute, ramie, kenaf,bagasse, bamboo, or reed.

Advantageously, at least 30 wt. % or at least 40 wt. %, more preferablyat least 50 wt. % or at least 60 wt. %, and most preferably at least 80wt. % or at least 90 wt. % of the organic natural fiber material is woodbased. Advantageously, at least 30 wt. % or at least 40 wt. %, morepreferably at least 50 wt. % or at least 60 wt. %, and most preferablyat least 80 wt. % or at least 90 wt. % of the organic natural fibermaterial comes from hardwood. In this case, preferably at least 30 wt. %or at least 40 wt. %, more preferably at least 50 wt. % or at least 60wt. %, and most preferably at least 80 wt. % or at least 90 wt. % of thehardwood is birch and/or eucalyptus. Alternatively or in addition, atleast 30 wt. % or at least 40 wt. %, more preferably at least 50 wt. %or at least 60 wt. %, and most preferably at least 80 wt. % or at least90 wt. % of the organic natural fiber material comes from softwood.However, the total amount of the softwood and the hardwood in theorganic natural fiber material is not more than 100 wt. %. Preferably,at least 30 wt. % or at least 40 wt. %, more preferably at least 50 wt.% or at least 60 wt. %, and most preferably at least 80 wt. % or atleast 90 wt. % of the softwood is pine or spruce.

The organic natural fiber material can be in the form of fibers, such asfloccules, single fibers, or parts of single fibers, or the organicnatural fiber material can be in the form of fiber-like particles, suchas saw dust or grinded material, where the material does not have anexactly spherical form, but the longest dimension of particle ispreferably less than 5 times longer than the smallest dimension.

Preferably the organic natural fiber material is, at least partly, inthe form of fibers. Preferably at least 40 wt. % or at least 50 wt. %,more preferably at least 60 wt. % or at least 70 wt. % and mostpreferably at least 80 wt. % of the organic natural fiber materials arein the form of fibers. In this application, the organic natural fibermaterial having a length of at least 0.1 mm, more preferably at least0.2 mm and most preferably at least 0.3 mm are called fibers, andsmaller particles than those mentioned above are called powder orfiber-like particles. Preferably at least 70%, at least 80% or at least90% of the organic natural fiber material has a length weighted fiberlength of under 4 mm, under 3 mm or under 2.5 mm, more preferably under2.0 mm, under 1.5 mm, under 1.0 mm or under 0.5 mm. Preferably, at least70%, at least 80%, or at least 90% of the organic natural fiber materialhas a length weighted fiber length of at least 0.1 mm or at least 0.2mm, more preferably at least 0.3 mm or at least 0.4 mm. Advantageously,the fiber has a shape ratio relating to the ratio of the fiber length tothe fiber thickness being at least 5, preferably at least 10, morepreferably at least 25 and most preferably at least 40. In addition oralternatively, the fiber has a shape ratio relating to the ratio of thefiber length to the fiber thickness being preferably 1500 at the most,more preferably 1000 at the most, and most preferably 500 at the most.In an example, the fiber length is measured using a so-called Fiberlabmeasuring device, manufactured by Metso.

Advantageously, the organic natural fiber material 11, 11 a comprisesfibers in a flake form. Flakes are fibers having a width that is atleast 2 times larger than the thickness of the fibers. Advantageously,the width of the flake is at least 2, preferably at least 2.5, and morepreferable at least 3 times the thickness of the flake. Preferably, theflakes have a thickness between 1 micron and 30 micrometers and morepreferably the thickness of flakes varies from 2 microns to 20micrometers. Most preferably the thickness of flakes is under 15 μm,more preferable under 10 μm and most preferable under 7 μm. In oneembodiment, the width of the flake is under 500 μm, preferably under 200μm, and more preferable under 50 μm. Preferably, an aspect ratiorelating to the ratio of the length to the width is between 10 and 100.Preferably, an aspect ratio relating to the ratio of the length to thethickness is less than 1500 or less than 1000, more preferable less than500 and most preferably between 25 and 300. In one embodiment, thelength of the flake is at least 10 times the width of the flake. In oneembodiment the flake has a tabular shape. In one embodiment the flakehas a platy shape. In one embodiment, the organic natural fiber materialcontains flake-form fiber material at least 30 dry wt. %, preferably atleast 50 dry wt. % and more preferable at least 70 dry wt. % of thetotal amount of the organic natural fiber material.

The organic natural fiber material may comprise mechanically treatedand/or chemically treated fibers and/or fiber-like particles.

The mechanically treated organic natural fiber material may comprise,among other things, wood flour, saw dust, chip material, and/ormechanical pulp such as TMP (thermo mechanical pulp), GW (groundwoodpulp)/SGW (stone groundwood pulp), PGW (pressure groundwood pulp), RMP(refiner mechanical pulp), and/or CTMP (chemithermomechanical pulp). Themechanically treated organic natural fiber material preferably comprisesor consists of wood particles, such as wood fibers, but they may alsocomprise or consist of non-wood material. The mechanically treatedorganic natural fiber material may comprise recycled and/or virginparticles, such as fibers or fiber-like particles. Advantageously atleast 30 wt. % or at least 40 wt. %, more preferably at least 50 wt. %or at least 60 wt. %, and most preferably at least 80 wt. % or at least90 wt. % of the organic natural fiber material used are virgin.Typically, for example, wood plastic composites (WPC) comprise saw dustor at least other mechanically treated wood or plant particles as mainorganic natural fiber material.

The chemically treated organic natural fiber material preferablycomprises chemical pulp. The chemical pulp may be, for example, fromkraft process or sulfite process, but also other chemical processes maybe used, such as a soda pulping process. Preferably, the chemical pulpis from the kraft process. The chemically treated organic natural fibermaterial preferably comprises or consists of wood based cellulose, butit may also be non-wood material. The chemically treated organic naturalfiber material may comprise recycled and/or virgin fibers and/orfiber-like particles. Advantageously, at least 30 wt. % or at least 40wt. %, more preferably at least 50 wt. % or at least 60 wt. %, and mostpreferably at least 80 wt. % or at least 90 wt. % of the organic naturalfiber material used is chemically treated particles. Advantageously, atleast 30 wt. % or at least 40 wt. %, more preferably at least 50 wt. %or at least 60 wt. %, and most preferably at least 80 wt. % or at least90 wt. % of the chemically treated particles used are from kraftprocess. Advantageously, lignin content of the chemically treated pulpis under 15 wt. %, preferably under 10 wt. % or under 5 wt. %, morepreferably under 3 wt. %, under 2 wt. % or under 1 wt. % and mostpreferably under 0.5 wt. %.

Preferably, the alfa cellulose content of the chemically treated pulp isabove 50 wt. %, preferably above 60 wt. %, more preferably above 70 wt.% and most preferably above 72 wt. % or above 75 wt. %. Advantageously,the alfa cellulose content of the chemically treated pulp is below 99wt. %, preferable below 90 wt. %, more preferably below 85 wt. % andmost preferably below 80 wt. %.

Advantageously at least 30 wt. % or at least 40 wt. %, more preferablyat least 50 wt. % or at least 60 wt. %, and most preferably at least 80wt. % or at least 90 wt. % of the organic natural fiber material usedare virgin.

Advantageously, lignin content of the organic natural fiber material isunder 15 wt. %, preferably under 10 wt. % or under 5 wt. %, morepreferably under 3 wt. % or under 1 wt. % and most preferably under 0.5wt. %. The lignin content may be low due to delignification process, orthe lignin content of the organic natural fiber material may benaturally on a low level. Advantageously, the lignin content of theorganic natural fiber material is at least 0.05 wt. %, more preferablyat least 0.10 wt. % or at least 0.2 wt. % and most preferably at least0.3 wt. %. In an embodiment, lignin content of the organic naturalmaterial is more than 3 wt. %, more than 5 wt. % or more than 10 wt. %.

In an embodiment, at least part of the organic natural fiber material isin the form of paper sheet or web, board sheet or web, pulp sheet orweb, or compacted fiber matrix or pieces of compacted fibers and theircombinations.

In an embodiment, at least part of the organic natural fiber material isin the form of large fiber or fiber bundles, paper chaff, pulp chaff,crushed pulp material, derivates thereof and their combinations.

In an embodiment, at least part of the organic natural fiber material isin the form of viscose fibers. However, preferably the amount of theorganic natural fiber material is calculated as the total amount of theuntreated and/or in the above-mentioned way mechanically treated, and/orin the above-mentioned way chemically treated organic natural fibermaterial in the system or product, and does not comprise the viscosefibers. Advantageously the amount of the viscose fibers is less than 5wt. % or less than 4 wt. %, more preferably less than 3 wt. % or lessthan 2 wt. %, and most .preferably less than 1 wt. %, less than 0.5 wt.% or less than 0.1 wt. % calculated from the total amount of the organicnatural fiber material.

In this application, the term “matrix material 12” means material whichcan preferably be several times formed into a new shape when it isheated. This material keeps its new shape after cooling and then itflows very slowly, or it does not flow at all. The matrix material hasat least one repeat unit, and molecular weight of the matrix material isover 18 g/mol, preferably over 100 g/mol, over 500 g/mol, or over 1000g/mol, more preferably over 10 000 g/mol or over 100 000 g/mol.

The matrix material 12 comprises preferably thermoplastic material;hence, the matrix material includes thermoplastic components.Advantageously, the amount of the thermoplastic material in the matrixmaterial is at least 80 wt. %, more preferably at least 90 wt. %, andmost preferably at least 95 wt. %. Advantageously, the matrix materialcomprises at least one crystalline polymer and/or at least onenon-crystalline polymer, and/or at least one crystalline oligomer and/orat least one non-crystalline oligomer.

Advantageously, the matrix material comprises, in addition to thethermoplastic polymers, polymeric coupling agent(s). Polymeric couplingagent preferably contains moiety or moieties, which are reactive or atleast compatible with the matrix material and moiety or moieties, whichare reactive or at least compatible with the organic natural fibermaterial. If the matrix material is non-polar, the moiety or moieties,which are reactive or compatible with the matrix material, arepreferably non-polar. If the matrix material is polar, the moiety ormoieties, which are reactive or compatible with the matrix material,is/are preferably polar. Preferable polymeric coupling agent containsthe same repeat units as the matrix material used. Advantageously atleast 30 wt. % or at least 40 wt. %, more preferably at least 50 wt. %or at least 60 wt. %, and most preferably at least 80 wt. % or at least85 wt. % of the moieties of the polymeric coupling agent are chemicallythe same as in the matrix material. Advantageously said moiety ormoieties which is/are reactive or at least compatible with the organicnatural fiber material comprise(s) anhydride(s), acid(s), alcohol(s),isocyanate(s), and/or aldehyde(s). Preferably, the coupling agent isacrylic acid grafted polymer. Alternatively or in addition, the couplingagent is methacrylic acid grafted polymer. Most preferably, the couplingagent comprises or consists of maleinic acid anhydride grafted polymer.The coupling agent can, in principle, be any chemical which is able toimprove the adhesion between two main components. This means that it maycontain components, which are known to be reactive or compatible withmatrix material and components, which are known to be reactive orcompatible with the organic natural fiber material.

Advantageously the coupling agent comprises or consists of

-   -   anhydrides, preferably maleic anhydride (MA),    -   polymers and/or copolymers, preferably maleated polyethylene        (MAPE), Maleated polypropylene (MAPP),        Styrene-ethylene-butylene-styrene/maleic anhydride (SEBS-MA),        and/or Styrene/maleic anhydride (SMA), and/or    -   organic-inorganic agents, preferably silanes and/or        alkoxysilanes.

Preferably, at least 50 wt. %, at least 60 wt. %, more preferably atleast 70 wt. % or at least 80 wt. % and most preferably at least 90 wt.% of the coupling agents used are

-   -   anhydrides, preferably maleic anhydride (MA), and/or    -   polymers and/or copolymers, preferably maleated polyethylene        (MAPE), Maleated polypropylene (MAPP),        Styrene-ethylene-butylene-styrene/maleic anhydride (SEBS-MA),        and/or Styrene/maleic anhydride (SMA), and/or    -   Organic-inorganic agents, preferably silanes and/or        alkoxysilanes.

Advantageously, the matrix material 12 comprises thermoplastic polymerbased matrix material and/or thermoplastic oligomer based matrixmaterial. Thermoplastic polymers are often solid at the low temperatureand they form viscose polymer melt at the elevated temperatures.Typically the viscosity of these polymer decreases when temperature isincreased, and the polymers flow and wet the surfaces more easily. Whenthermoplastic composites are produced, polymer is heated in order tomelt the polymer, and other components of the composites are mixed withthe polymer melt. Often it is easy to mix these other components intopolymer when the viscosity of the polymer is low, meaning that thetemperature of the polymer melt is high.

The matrix material is, at least partly, in melt form, when

-   -   the organic natural material can adhere to the matrix material,        and/or    -   the melt flow index of the material can be measured (according        to standard ISO 1133 (valid in 2011)), and/or    -   the organic natural fibre material can adhere to the surfaces of        matrix material particles.

Preferably at least 10% or at least 30%, more preferably at least 50% orat least 70% and most preferably at least 80% or at least 90% of thematrix material is in melt form in the contacting step of the primarymixing stage.

Preferably, at least 20% or at least 40%, more preferably at least 60%or at least 80% and most preferably at least 90% or at least 95% of thematrix material is in melt form at least momentarily during the primarymixing stage.

The polymer based matrix material contains one or more polymers, and theoligomer based matrix material contains one or more oligomers. The totalamount of the polymers and oligomers calculated from the total amount ofthe matrix material is preferably at least 80 wt. %, at least 85 wt. %,at least 90 wt. %, at least 95 wt. % or at least 98 wt. %.

If the matrix material comprises polymer, it may be any suitable polymeror polymer composition. Advantageously, the matrix material contains atleast 50 wt. %, at least 60 wt. %, more preferably at least 70 wt. %, orat least 80 wt. %, and most preferably at least 90 wt. % or at least 95wt. %:

-   -   polyolefin, e.g. polyethylene and polypropylene,    -   polystyrene,    -   polyamide,    -   polyester,    -   ABS (acrylic nitrile butadiene styrene copolymer),    -   polycarbonate,    -   biopolymer, e.g. polylactide,    -   biodegradable polymer,    -   bio-based polymer,    -   thermoplastic elastomer,    -   polysaccharides,    -   lignin, and/or    -   their derivatives.

The matrix material 12 may contain one or more polymer materialcomponents. Advantageously, at least one polymer is selected from thegroup consisting of polyethylene, polypropylene and their combinations.Advantageously, the amount of polypropylene and polyethylene in thematrix material is at least 50 wt. %, at least 60 wt. %, at least 70 wt.%, at least 80 wt. %, at least 90 wt. % or at least 95 wt. %.

Advantageously, the melting point of the matrix material is under 250°C., preferably under 220° C., and more preferable under 190° C.Advantageously, the glass transition temperature of the matrix materialis under 250° C., preferably under 210° C., and more preferable under170° C.

Advantageously, melt flow rate, MFR, of the matrix material is under1000 g/10 min (230° C., 2.16 kg defined by ISO 1133, valid 2011), morepreferable 0.1-200 g/10 min, most preferable 0.3-150 g/10 min.Advantageously, melt flow rate, MFR, of the matrix material is over 0.1g/10 min (230° C., 2.16 kg defined by ISO 1133, valid 2011), morepreferable over 1 g/10 min, most preferable over 3 g/10 min.

FIGS. 1 to 6 show reduced flow chart illustrations of some exampleembodiments of the present invention.

In FIG. 1, the organic natural fiber material 11, 11 a is first crushedin a pre-crushing stage 23 comprising a crusher 28, after which it istreated in a pre-separation stage 24 comprising a separator 29. Theformed bulky organic natural fiber material 11 a is combined with thematrix material 12 in a primary mixing stage 36, 38 in order to form amixture 15. A composite product 40, 40 a, 40 b is formed, whichcomposite product comprises the mixture 15.

In FIG. 2 the organic natural fiber material 11, 11 a is first crushedin a pre-crushing stage 23, 28, after which the bulky organic naturalfiber material 11 a is combined with the matrix material 12 in a primarymixing stage 36, 38 in order to form a mixture 15. A composite product40, 40 a, 40 b is formed, which composite product comprises the mixture15.

In FIG. 3 the organic natural fiber material 11, 11 a is first crushedin a pre-crushing stage 23, after which the bulky organic natural fibermaterial 11 a is combined with the matrix material 12 in a primarymixing stage 36, 38 in order to form a mixture 15. A composite product40, 40 a, 40 b comprising the mixture 15 is formed in at least twoprocess steps 39 a, 39 b.

In FIG. 4 the organic natural fiber material 11, 11 a is first mixed ina pre-mixing stage 21, 21 a, 27, after which the bulky organic naturalfiber material 11 a is combined with a solid matrix material 12 in thesecond pre-mixing stage 21, 21 b, 27. The solid matrix material 12 isthen at least partly melted and the matrix material and the bulkyorganic natural fiber material 11 a are mixed with each other in aprimary mixing stage 36 a-b, 38 in order to form a mixture 15. Acomposite product 40 is formed, which composite product comprises themixture 15.

In FIG. 5 the organic natural fiber material 11, 11 a is firstpre-treated in a pre-treatment stage 20, 25, after which the bulkyorganic natural fiber material 11 a is combined with the matrix material12 in the primary mixing stage 30, 36 a-b, 38 in order to form themixture 15. In addition, a composite product 40 a, 40 b comprising themixture 15 is formed.

In FIG. 6, the bulky organic natural fiber material 11, 11 a is combinedwith the matrix material 12 in a primary mixing stage 36, 38 comprisingmeans 39, such as an extruder, for forming a composite product 40, 40 a,40 b.

Advantageously, the matrix material 12 is mixed with the organic naturalfiber material 11, 11 a in a primary mixing stage 36. The primary mixingstage 36 comprises a contacting step 36 a wherein at least partly meltedmatrix material contacts the organic natural fiber material, and amixing step 36 b, in which the at least partly melted matrix material ismixed with the organic natural fiber material. Advantageously, theorganic natural fiber material used is bulky before it is mixed with theat least partly melted matrix material.

The term “bulky” can be defined as certain bulk density of the organicnatural fiber material. Bulk density is defined as the mass of particlesthat occupies a unit volume of a container. Bulk density of granular andpowdery materials can be determined by the ratio of the mass to a givenvolume. Determination of bulk density can be done, for example, byfilling a container of known dimensions and weight with the material ofinterest and by weighing the container containing the material ofinterest. Bulk density depends on particle size, particle form, materialcomposition, moisture content, as well as on material handling andprocessing operations. For example, rounded particles will be closertogether when poured into a container compared to non-sphericalparticles, such as fibers.

In this application, the bulk density means

-   -   1) apparent bulk density of the organic natural fiber material,        and    -   2) calculated bulk density of the organic natural fiber        material.

The apparent bulk density is measured bulk density of the organicnatural fiber material, and it is typically neither compressed nordecompressed. The calculated bulk density depends on the amount oforganic natural fiber material in a certain volume, and it comprisesalso compressed and decompressed bulk densities.

Bulk density ρ of the organic natural fiber material is calculated bydividing the weight of the sample by its volume as follows:

$\begin{matrix}{\rho = \frac{{mass}\mspace{14mu}{of}\mspace{14mu}{fibre}}{{volume}\mspace{14mu}{of}\mspace{14mu}{fibre}}} & {{Eq}.\mspace{14mu}(1)}\end{matrix}$

Organic fiber material is, however, very soft and bulky and that is whythe bulk density can be increased a great deal by compressing orpressing the organic natural fiber material.

The determination of bulk density can be done, for example, according toISO 697 and ISO 60 (valid 2011), and their counterparts in otherstandards organizations, and by other similar measurement proceduresthat would ensure reasonable results in the determination of bulkdensity. In addition, bulk density can be determined with devices suchas Powder Characteristics Tester by Hosokawa and Powder Flow Tester byBrookfield, and with other similar devices intended for determination ofdifferent characteristics of powdery materials. Bulk density can also bemeasured by suitable laboratory and on-line measurement sensorsincluding, but not limited to, techniques based on microwaves. Bulkdensity of organic natural fiber material can be determined as describedabove. Preferably, the bulk density values are measured according toExample 21.

Calculated bulk density ρ_(calculated) is the bulk density the organicfiber material would have, if the material would be evenly distributedto the volume that is available at given time. Calculated bulk densityρ_(calculated) of fiber for batch, i.e. discontinuous, process can bedetermined as follows:

$\begin{matrix}{{\rho_{calculated} = \frac{{mass}\mspace{14mu}{of}\mspace{14mu}{fibre}}{{available},{{free}\mspace{14mu}{volume}\mspace{14mu}{of}\mspace{14mu}{mixer}}}}{{and}\mspace{14mu}{for}\mspace{14mu}{continous}\mspace{14mu}{process}\mspace{14mu}{like}\mspace{14mu}{this}\text{:}}} & {{Eq}.\mspace{14mu}(2)} \\{\rho_{calculated} = \frac{{mass}\mspace{14mu}{flow}\mspace{14mu}{of}\mspace{14mu}{fibre}}{{conveying}\mspace{14mu}{volumetric}\mspace{14mu}{flow}\mspace{14mu}{of}\mspace{14mu}{mixer}}} & {{Eq}.\mspace{14mu}(3)}\end{matrix}$

Advantageously, bulk density of the organic natural fiber material (i.e.calculated bulk density and/or apparent bulk density) before thecontacting step is under 800 kg/m³, under 700 kg/m³, under 500 kg/m³,under 300 kg/m³, or under 250 kg/m³, more preferably under 200 kg/m³,under 180 kg/m³, or under 150 kg/m³. Most advantageously, bulk densityof the organic natural fiber material is at least 10 kg/m³, at least 15kg/m³, or at least 20 kg/m³, more preferably at least 30 kg/m³, or atleast 40 kg/m³, and most preferably at least 50 kg/m³. Alternatively orin addition, bulk density of the organic natural fiber material is atleast 10 kg/m³, at least 15 kg/m³, or at least 20 kg/m³, more preferablyat least 30 kg/m³, or at least 40 kg/m³, and most preferably at least 50kg/m³. Then the organic natural fiber material can be incorporated tomatrix material easily.

Compression ratio R can be calculated if calculated bulk density andapparent bulk density are known. Compression ratio R can be calculatedaccording to equation:

$\begin{matrix}{R = \frac{\rho_{calculated}}{\rho}} & {{Eq}.\mspace{14mu}(4)}\end{matrix}$

where ρ_(calculated) is the calculated bulk density of organic naturalfiber material and ρ is the apparent bulk density of organic naturalfiber material. Herein, the mass of fiber and mass flow of fiber arebased on the dry mass of the fibers, i.e. the amount of moisture presentin the organic natural fiber material is subtracted in the measurementsand calculations.

The compression ratio R of the organic natural fiber material is often avery important feature because, until the fibers are at least partlysurrounded by the matrix material, the organic natural fibers willcreate bonds with each other and, hence, form flocks. These organicnatural fiber material flocks may decrease the quality of themanufactured composite product comprising said organic natural fibermaterial. Many other fiber materials, such as glass fibers, do notcreate similar bonds and flocks under pressure and, thus, thisphenomenon is not as important for them as for the organic natural fibermaterial.

If the compression ratio R of the organic natural fiber material in thecontacting step of the primary mixing stage is large, the contacting ofthe organic natural fiber material and the matrix material is made withsome compression to the fibers. This may make the conditions unfavorablefor good wetting of fibers, and thus dispersion of fibers to matrix istypically poor.

Therefore, the compression ratio R of the organic natural fiber materialcomposition in the contacting step 36 a of the primary mixing stage 36is preferably less than 8, less than 7 or less than 6, more preferablyless than 5 or less than 4, and most preferably less than 3 or less than2.

Advantageously, the compression ratio R of the organic natural fibermaterial 11, 11 a in the contacting step 36 a of the primary mixingstage 36 is not more than 8, for example between 0.2 and 8, morepreferably not more than 6, for example between 0.2 and 6 or between 0.5and 6,and most preferably not more than 4, for example between 0.2 and 4or between 0.8 and 4 when the apparent bulk density is 0<bulk density<20g/l.

Alternatively or in addition, the compression ratio R of the organicnatural fiber material 11, 11 a in the contacting step 36 a of theprimary mixing stage 36 is not more than 8, for example between 0.2 and8, more preferably not more than 6, for example between 0.2 and 6 orbetween 0.5 and 6, and most preferably not more than 4, for examplebetween 0.2 and 4 or between 0.8 and 4 when the calculated bulk densityis 0<bulk density<20 g/l.

Advantageously, the compression ratio R of the organic natural fibermaterial in the contacting step of the primary mixing stage is not morethan 6, for example between 0.2 and 6, more preferably not more than 4,for example between 0.2 and 4 or between 0.5 and 4, and most preferablynot more than 3, for example between 0.2 and 3 or between 0.8 and 3,when the apparent bulk density is 20≤bulk density<40 g/l.

Alternatively or in addition, the compression ratio R of the organicnatural fiber material in the contacting step of the primary mixingstage is not more than 6, for example between 0.2 and 6, more preferablynot more than 4, for example between 0.2 and 4 or between 0.5 and 4, andmost preferably not more than 3, for example between 0.2 and 3 orbetween 0.8 and 3, when the calculated bulk density is 20≤bulkdensity<40 g/l.

Advantageously, the compression ratio R of the organic natural fibermaterial in the contacting step of the primary mixing stage is not morethan 4, for example between 0.2 and 4.0, more preferably not more than3, for example between 0.2 and 3.0 or between 0.5 and 3.0, and mostpreferably not more than 2.5, for example between 0.2 and 2.5 or between0.8 and 2.5 when the apparent bulk density is 40≤bulk density<80 g/l.

Alternatively or in addition, the compression ratio R of the organicnatural fiber material in the contacting step of the primary mixingstage is not more than 4, for example between 0.2 and 4.0, morepreferably not more than 3, for example between 0.2 and 3.0 or between0.5 and 3.0 and most preferably not more than 2.5, for example between0.2 and 2.5 or between 0.8 and 2.5 when the calculated bulk density is40≤bulk density<80 g/l.

Advantageously, the compression ratio R of the organic natural fibermaterial in the contacting step of the primary mixing stage is not morethan 3.0, for example between 0.2 and 3.0, more preferably not more than2.5, for example between 0.2 and 2.5 or between 0.5 and 2.5 and mostpreferably not more than 2.0, for example between 0.2 and 2.0 or between0.8 and 2.0 when the apparent bulk density is 80≤bulk density<150 g/l.

Alternatively or in addition, the compression ratio R of the organicnatural fiber material in the contacting step of the primary mixingstage is not more than 3.0, for example between 0.2 and 3.0, morepreferably not more than 2.5, for example between 0.2 and 2.5 or between0.5 and 2.5 and most preferably not more than 2.0, for example between0.2 and 2.0 or between 0.8 and 2.0 when the calculated bulk density is80≤bulk density<150 g/l.

Advantageously, the compression ratio R of the organic natural fibermaterial in the contacting step of the primary mixing stage is not morethan 2.5, for example between 0.2 and 2.5, more preferably not more than2.0, for example between 0.2 and 2.0 or between 0.5 and 2.0 and mostpreferably not more than 1.5, for example between 0.2 and 1.5 or between0.8 and 1.5 when the apparent bulk density is 150≤bulk density<300 g/l.

Alternatively or in addition, the compression ratio R of the organicnatural fiber material in the contacting step of the primary mixingstage is not more than 2.5, for example between 0.2 and 2.5, morepreferably not more than 2.0, for example between 0.2 and 2.0 or between0.5 and 2.0 and most preferably not more than 1.5, for example between0.2 and 1.5 or between 0.8 and 1.5 when the calculated bulk density is150≤bulk density<300 g/l.

Advantageously, the compression ratio R of the organic natural fibermaterial in the contacting step of the primary mixing stage is not morethan 2.0, for example between 0.2 and 2.0, more preferably not more than1.5, for example between 0.2 and 1.5 or between 0.5 and 1.5 and mostpreferably not more than 1.2, for example between 0.2 and 1.2 or between0.8 and 1.2 when the apparent bulk density is at least 300 g/l, forexample between 300≤bulk density<700 g/l.

Alternatively or in addition, the compression ratio R of the organicnatural fiber material in the contacting step of the primary mixingstage is not more than 2.0, for example between 0.2 and 2.0, morepreferably not more than 1.5, for example between 0.2 and 1.5 or between0.5 and 1.5 and most preferably not more than 1.2, for example between0.2 and 1.2 or between 0.8 and 1.2 when the calculated bulk density isat least 300 g/l, for example between≤300 bulk density<700 g/l.

Advantageously, the calculated bulk density of the organic natural fibermaterial 11, 11 a in the contacting step 36 a of the primary mixingstage 36 is less than 80 g/l, more preferably less than 60 g/l and mostpreferably less than 40 g/l when the apparent bulk density is less than10 g/l.

Advantageously, the calculated bulk density of the organic natural fibermaterial in the contacting step of the primary mixing stage is less than160 g/l, more preferably less than 120 g/l and most preferably less than80 g/l when the apparent bulk density is between 10≤apparent bulkdensity<20 g/l.

Advantageously, the calculated bulk density of the organic natural fibermaterial in the contacting step of the primary mixing stage is less than240 g/l, more preferably less than 160 g/l and most preferably less than120 g/l when the apparent bulk density is between 20≤apparent bulkdensity<40 g/l.

Advantageously, the calculated bulk density of the organic natural fibermaterial in the contacting step of the primary mixing stage is less than320 g/l, more preferably less than 240 g/l and most preferably less than200 g/l when the apparent bulk density is between 40≤apparent bulkdensity<80 g/l.

Advantageously, the calculated bulk density of the organic natural fibermaterial in the contacting step of the primary mixing stage is less than450 g/l, more preferably less than 375 g/l and most preferably less than300 g/l when the apparent bulk density is between 80≤apparent bulkdensity<150 g/l.

Advantageously, the calculated bulk density of the organic natural fibermaterial in the contacting step of the primary mixing stage is less than750 g/l, more preferably less than 600 g/l and most preferably less than450 g/l when the apparent bulk density is between 150≤apparent bulkdensity<300 g/l.

Advantageously, the calculated bulk density of the organic natural fibermaterial in the contacting step of the primary mixing stage is less than1400 g/l, more preferably less than 1050 g/l and most preferably lessthan 840 g/l when the apparent bulk density is at least 300 g/l, forexample between 300≤apparent bulk density<700 g/l.

Advantageously, the calculated bulk density of the organic natural fibermaterial is less than 5 times the apparent bulk density, more preferablyless than 3.5 times and most preferably less than 2 times the apparentbulk density.

Advantageously, the calculated bulk density of the organic natural fibermaterial is at least 0.4 times the apparent bulk density, and preferablyat least 0.5 times and more preferable at least 0.6 times the apparentbulk density.

Advantageously, the method according to the present invention comprisesat least some of the following steps:

-   -   introducing the organic natural fiber material 11, 11 a to the        system,    -   introducing the matrix material 12 to the system,    -   pre-crushing 23 the organic natural fiber material before the        primary mixing stage to form a bulky material,    -   pre-separating 24 the organic natural fiber material before the        primary mixing stage 36,    -   pre-mixing 21, 21 a the organic natural fiber material before        the primary mixing stage 36,    -   treating chemically the organic natural fiber material before        the primary mixing stage 36,    -   pre-mixing 21, 21 b the organic natural fiber material and        unmelted matrix material before the primary mixing stage 36,    -   melting the matrix material at least partly,    -   contacting the at least partly melted matrix material with the        organic natural fiber material, the organic natural fiber        material being preferably bulky in the beginning of the        contacting step,    -   mixing the at least partly melted matrix material with the        organic natural fiber material in the primary mixing stage in        order to form a mixture,    -   forming 39 a composite product 40, 40 a, 40 b comprising the        mixture.

The matrix material 12 and the organic natural fiber material 11, 11 aare contacted with each other before a contacting step or in acontacting step 36 a of the primary mixing stage 36. If the matrixmaterial 12 and the organic natural fiber material 11, 11 a arecontacted before the contacting step 36 a of the primary mixing stage36, the contacting step does not start until the matrix material atleast starts to melt, i.e. at least 10 wt. % of the matrix material isin melt form.

Advantageously, the mixture 15 comprising organic natural fiber materialand the melted matrix material is formed so that the organic naturalfiber material has been incorporated to the melt matrix material withoutuse of compression during the contacting step. Preferably, the mixing ofthe primary mixing stage is made without the compression regardless ofmixing method and mixing type. However, in an embodiment, the compositeproduct is formed from the mixture under heat and pressure.

Advantageously, the composite product 40 comprising the mixture 15 isformed by a method selected from the group consisting of extrusion,granulation, mixing method, pelletization and their combinations. In oneembodiment, the composite product is formed by means of a mixing device,an internal mixer, a kneader, a pelletizer, a pultrusion method, a pulldrill method, and/or an extrusion device. Advantageously, the compositeproduct is formed by injection moulding. Alternatively or in addition,the composite product is formed by extrusion.

The matrix material 2 is arranged at least partly in the form of melt atleast in the contacting step of the primary mixing stage 36 a in whichthe organic natural fiber material comes in contact with the melt matrixmaterial. During the primary mixing stage 36, the organic natural fibermaterial becomes wet by the matrix material.

The contacting step 36 a means the process place or area, in which theorganic natural fiber material comes in contact with the at least partlymelted matrix material. Advantageously, the matrix material is in a meltform during the contacting step, i.e. the matrix material is arranged inthe form of melt at least in the contacting step in which the organicnatural fiber material comes in contact with the melt matrix material.Therefore, the matrix material is preferably heated so that thetemperature of the matrix material is higher than the glass transitiontemperature or, if the matrix material has a melting temperature, thematrix material is heated higher than the glass transition and meltingtemperatures, before the contacting step of the primary mixing stagestarts. In the melting, phase transition is from solid to melt.

The primary mixing stage is preferably a part of a continuous process.However, the primary mixing stage may also be implemented in a batchprocess.

The organic natural fiber material is preferably bulky, i.e. it is at apredetermined bulk density level before the contacting step of theprimary mixing stage starts.

Advantageously, the fibers of the organic natural fiber material arecrushed before the contacting step to form a bulky organic natural fibermaterial composition. Therefore, the organic natural fiber material ispreferably pre-crushed 23 by a crusher 28 before the primary mixingstage 36 in order to form bulky material 11 a. Advantageously, thepre-crushing 23 is implemented before other pre-treatments, such aschemical treatment 25 and/or pre-separation 24. Alternatively or inaddition, the pre-crushing is implemented after chemical treatment 25and/or pre-separation 24. In one embodiment, bundles of fibers aredischarged before the contacting step 36 a of the primary mixing stage36, which can be implemented by at least one crushing device 28.Advantageously, the fiber material is at least partly in the form offlakes after the crushing.

Technical effects of the bulky material are fluency and ability to flowand non-arching. In addition, the fibers and/or the fiber-like materialcan be spread evenly among the matrix material. Further, the wetting ofthe fibers can take place evenly.

The pre-crushing 23 can be made in one or more crushing steps by one ormore crushing methods. The crushing 23 can be made by any suitablemethod known to a person skilled in the art. In this context, thecrushing 23 means any crushing, grinding, fractionizing, pulverizing andtheir combinations.

In an embodiment, the organic natural fiber material is pre-crushed 23by crushing-based grinding, attrition-based grinding, abrasion-basedgrinding, cutting-based grinding, blasting-based grinding,explosion-based grinding, wet grinding, dry grinding, grinding underpressure or by their combinations. Preferably, the organic natural fibermaterial is crushed by a crushing-based grinding and/or by a cuttingbased grinding. Advantageously, the organic natural fiber material ispre-crushed 23 so that during the treatment the fibers are separated andcut. Therefore, most preferably the organic natural fiber material 1 iscrushed 23 by the cutting grinding.

Advantageously, an impact mill, an air jet mill, a sand mill, a beadmill, a pearl mill, a ball mill, a vibration mill, and/or a screw millis used for the pre-crushing 23.

Advantageously, the organic natural fiber material is pre-treated in atleast one pre-treatment stage 20. Preferably, the system comprises atleast one pre-treatment stage 20 before the contacting step 36 a of theprimary mixing stage 36. If the system comprises the pre-crushing stage23, there is preferably also at least one additional pre-treatment stage20 after the crushing step 23 but before the primary mixing stage 36.

In the pre-treatment stage(s), the organic natural fiber material is notin contact with the at least partly melted matrix material. Thus, theorganic natural fiber material and the matrix material are pre-treatedseparately, or only one of them is pre-treated, and/or the organicnatural fiber material is pre-treated with solid matrix material.

Instead of or in addition to the pre-crushing 23, the pre-treatmentstage(s) 20 may comprise, for example,

-   -   a drying step,    -   a pre-mixing step 21 a of the organic natural fiber material,    -   a pre-mixing step 21 b of the organic natural fiber material and        the unmelted matrix material,    -   a heating step,    -   a compacting step, and/or    -   a chemical pre-treatment step 25.

In one embodiment, the pre-treatment stage 20 contains heating, cooling,mixing, agglomeration, pre-granulation, and/or pelleting step. The orderof the pre-treatments may vary.

In one embodiment, the fiber material is pre-treated at ambient gaspressure less than 100 bar, more preferably less than 80 bar, less than60 bar, less than 50 bar, less than 40 or less than 30 bar or less than20 bar, more preferably less than 15 bar, less than 10 bar, less than 8bar, less than 6 bar, less than 4 bar or less than 3 bar and mostpreferably less than 2.5 bar or less than 2.0 bar. The pressure aroundthe organic natural fiber material (for example inside a closed vessel)may be quite high as long as the organic natural fiber material is notcompressed too much. In other words, typically the bulk density is theimportant thing, not simply the air pressure.

The pressure compressing the organic natural fiber material before thecontacting step of the primary mixing stage, i.e. the pressurecompressing the organic natural fiber material during the pre-treatment,is preferably less than 4 bar or less than 3 bar, more preferably lessthan 2.5 bar or less than 2.0 bar and most preferably less than 1.5 bar.

In an example embodiment, at least a part of the organic natural fibermaterial is pre-mixed 21, 21 a before the primary mixing stage 36 insuch way that fiber agglomerates are disintegrated as well as possiblebut the fibers are not cut during the mixing. Methods of pre-mixing mayinclude, but are not limited to, blenders, food mixers, concrete-mixers,and fluidization techniques. In one embodiment, the pre-mixing 21, 21 a,21 b is carried out by a heating mixer, a cooling mixer, an internalmixer, e.g. Banbury, a continuous mixer and/or some other suitabledevice.

In one embodiment, the matrix material is pre-mixed 21, 21 b with theorganic natural fiber material during a pre-treatment step 20. In thiscase, the matrix material is not melted but the materials are pre-mixedwith each other when the matrix material is in a solid form.

In one embodiment, the fibers of the organic natural fiber material arefirst pre-mixed 21 a with each other without compression of the fibermaterial, and the fiber material is then pre-mixed 21 b with theunmelted matrix material without compression so that the mixing of theorganic natural fiber material and the matrix material is made withoutforming of the bonds between fibers of the organic natural fibermaterial.

In one embodiment, the fibers of the organic natural fiber material arepre-treated with chemical(s) 25, preferably without a heavy compression,in order to improve adhesion. Preferably lubricant(s), waxe(s),compatibilization agent(s), ionic surfactant(s), non-ionicsurfactant(s), silane(s), acid anhydride(s) and/or carboxylic acid(s) isused for the chemical pretreatment.

Alternatively or in addition, another chemical(s), which improves thewetting of fibers or adhesion between the organic natural fiber materialand the matrix material may be used, especially if the chemical is inliquid form or in gas form or in melt form below temperatures where thematrix material is in solid form.

Advantageously, the pre-treatment 20 comprises a drying step, in whichdry matter content of the organic natural fiber material is increased.Preferably, after the pre-treatment, the moisture content of the organicnatural fiber material is preferably less than 7%, less than 6%, lessthan 5%, less than 4%, or less than 3%, more preferably less than 2.5%,less than 2.0%, less than 1.5% or less than 1.0%, and most preferablyless than 0.8% or less than 0.5%.

In an example, the pre-treatment 20 comprises the chemical treatment 25and the drying steps and the chemical treatment is implemented before orduring the drying step.

Advantageously, the fibers of the organic natural fiber material areseparated (i.e. classified/sorted) in a pre-separation stage 24 beforethe contacting step 36 a of the primary mixing stage and before thewetting of the fibers therein.

In this application, the primary mixing stage 36 means a process stepwhich starts when the organic natural fiber material comes in contactwith the matrix material that is at least partly in melt form and stopswhen the organic natural fiber material has become wet by the matrixmaterial in whole or substantially in whole, or the surfaces of theorganic fiber material are covered by the matrix material so much thatthe adhesion of fibers is prevented, when the material is pressedafterwards. Preferably, at least 40% or at least 50%, more preferably atleast 60% or at least 70% and most preferably at least 80% or at least90% of the surface area of the organic natural fiber material arecovered by the matrix material after the primary mixing stage 36 and inthe composite product 40.

Therefore, the primary mixing stage 36 and the contacting step 36 atherein starts when the organic natural fiber material 11, 11 a and thematrix material 12 are in contact with each other and the matrixmaterial is melted or starts to melt and, hence, the primary mixingstage 36 starts when the matrix material starts to wet the surfaces ofthe organic natural fiber material. Therefore, it is possible that theorganic natural fiber material and the matrix material are in contactwith each other already before the primary mixing stage if the matrixmaterial is in solid form.

Preferably, the primary mixing stage continues at least until thepolymer is totally melted. In other words, the mixing continues at leastuntil the fibers of the organic natural fiber material cannot bound witheach other anymore. The fiber material and additives are now dispersedwith the polymer melt. During the forming of the composite product 40,the homogeneous composite material is preferably cooled until thematerial is totally solid.

The moisture content of the natural organic fiber material in thecontacting step 36 a and/or just before the contacting step ispreferably less than 7%, less than 6%, less than 5%, less than 4%, orless than 3%, more preferably less than 2.5%, less than 2.0%, less than1.5% or less than 1.0%, and most preferably less than 0.8% or less than0.5%. A technical effect of this is that the wetting of the organicnatural fiber material and mixing and adhesion between the matrixmaterial and organic natural fiber material can be improved and theflocculation of the organic natural fiber material may be avoidedbecause in this case the coupling agent may not react first with waterbut it reacts with the organic natural fiber material.

The organic natural fiber material is mixed with the melted matrixmaterial to form a mixture comprising at least said organic naturalfiber material and the matrix material. Advantageously, the matrixmaterial is in the form of melt during the mixing 36 b until asubstantial amount, preferably at least 30%, at least 40%, at least 50%,at least 60%, at least 70%, at least 80% or at least 90% of fibersurfaces are wet by the matrix material.

Preferably, such pressure is used that bonds between fibers are notformed, i.e. the mixing of the fiber based starting material and matrixmaterial is made without forming of the bonds between fibers of thefiber material. In a preferred embodiment, the fiber material isincorporated to matrix material at least without or with a smallcompression and preferably also without pressure substantially overatmospheric pressure. Advantageously, the fiber material is mixed withmatrix material without compression to form a mixture.

Pressure compressing the organic natural fiber material during thecontacting step of the primary mixing stage is preferably less than 5bar, less than 4 bar or less than 3 bar, more preferably less than 2.5bar, less than 2.0 bar, less than 1.5 bar or less than 1.0 bar and mostpreferably less than 0.5 bar, less than 0.3 bar, less than 0.2 bar orless than 0.1 bar.

Preferably, the organic natural fiber material is mixed lightly with thematrix material in the primary mixing stage 36 in order to form themixture so that the mixing is made without heavy compression, and theorganic natural fiber material is evenly distributed to a mixing volume,preferably to a free volume of a mixing area.

For example, a Z-blade mixer, a batch type internal mixer, an extruder,a heating mixer and/or a heating/cooling mixer is used for the mixingstep 36 b of the primary mixing stage. Advantageously a mixer comprisinga heating section is used. The mixer preferably comprises a sectionwherein at least some of the moisture coming from the raw materials canbe removed. The organic natural fiber material and the matrix materialcan be mixed and agglomerated to a homogeneous or substantiallyhomogeneous mixture. The fiber content may be adjustable within a widerange, and high contents may be easy to achieve.

Suitable and desired additives can be added into the organic naturalfiber material, the matrix material and/or the mixture comprising thematrix material and the organic natural fiber material. Advantageously,at least one additive comprising

-   -   property enhancers,    -   coupling agent,    -   adhesion promoter,    -   lubricant,    -   rheology modifiers,    -   releaser agent,    -   fire retardant,    -   coloring agent,    -   anti-mildew compound,    -   protective agent,    -   antioxidant,    -   uv-stabilizer,    -   foaming agent,    -   curing agent,    -   coagent, and/or    -   catalyst        is used.

Advantageously, at least one filler comprising fibrous material, organicfillers like starch or protein or some organic residues, inorganicfillers, powdery reinforcements, calcium carbonate and/or talc is used.The total amount of the fillers is preferably less than 50 wt. %, morepreferably less than 40 wt. %, and most preferably less than 30 wt. %calculated from the total weight of the composite product.

Advantageously, at least one additive and/or at least one filler areadded into the mixture comprising the organic natural fiber material andthe matrix material. Most advantageously, coupling agent is polymericcoupling agent which is included in the matrix material.

In one embodiment of the invention, the organic natural fiber materialis at least partly in the form of flakes before the contacting step ofthe primary mixing stage. In one embodiment, any flake-form fibermaterial can be used as an organic natural fiber material or as a partof an organic natural fiber material.

Advantageously, in the primary mixing stage and at least in thecontacting step of the primary mixing stage, the materials arepreferably mixed in vacuum or in the presence of gas. If gas is used,advantageously the gas comprises or consists of air and/or nitrogenand/or helium.

In one embodiment, the composite product 40 is in the form of particles.This kind of composite product is typically an intermediate compositeproduct 40 a. In this application, the composite particle refers to anygranulate, agglomerate, pellet or the like. The composite product in theform of particles is preferably formed by a granulation method, apelleting method, an agglomeration method or their combinations.

Advantageously, the composite product 40, 40 a, 40 b is in the form ofgranulates. In one embodiment, the granulation is carried out by meansof a method selected from the group consisting of water ring, underwaterpelleting, air cooled, hot face strand, and their combinations. In oneembodiment the granulation is made under water. In one embodiment thegranulation is carried out by means of counterpressure, e.g. withunderwater method.

In one embodiment, the granulates are formed directly from the mixture15 comprising the organic natural fiber material and the matrix materialby extrusion or by any other suitable process. In one embodiment, thegranulates are formed from an intermediate composite product 40 a, whichintermediate composite product is formed from the mixture 15 byextrusion or by any other suitable process.

The main task of granulating, or pelleting, is to produce homogeneousfree-flowing granulates, typically for further processing. In severalprocesses, e.g. extrusion and injection moulding, easily dosablegranulates are required for good production. Pre-granulation is oftenmore important when organic natural fibers are used. Natural fiberplastic granulates can be manufactured with different methods.

Production of granulates may have two important targets: compounding andforming of granulates. These can be made with one machine or withdifferent machines. The simplest way to produce natural fiber-polymergranulates is to use one machine or one machine combination whichcompounds material components and forms this material to granulates. Oneexample of this kind of machine is a compounding twin screw extruderwith granulation tool.

The apparatus 39 for forming the composite product may also be used forthe primary mixing stage 36. The apparatus 39 for forming the compositeproduct is preferably an extruder.

In the case of composite particles, the material components may be fedinto a compounding extruder at the beginning of the screws so meltingcan start as soon as possible. Material components could be, forexample, the matrix material, e.g. plastic, the natural organic fibermaterial, additives and fillers.

In some cases, the organic natural fiber material or a part of it can befed later to avoid fiber break-ups. Adding fibers later, for example,into extruder, can also affect dispersion of fibers and plastic. Polymeris often melted mainly with friction, but some external heat can beused. Polymer, additives and fibers are preferably mixed when they aremoving through a screw barrel. Melt compound may be pressed through agranulation tool, which is, for example, underwater pelletizer, andgranulate is formed.

The composite product 40 and compounding of the materials are preferablyformed with an extruder. Extruders can be divided into single, twin ormultiple screw machines. The single screw can be with a smooth, groovedor pin barrel machine. The twin screw extruder can be a conicalco-rotating twin screw extruder, a conical counter-rotating twin screwextruder, a parallel co-rotating twin screw extruder, or a parallelcounter-rotating twin screw extruder. The multiple screw extruders canbe with a rotating or static center shaft.

In addition or alternatively, the composite product 40 and compoundingof the materials can be formed with mixers like internal mixer,heating-cooling mixer or z-blade mixer, or with any mixing device wherepolymer is melted with friction or internal and/or external heat andfibers are incorporated to polymer and other components. The mixing canbe a batch or continuous process. The mixing can take place in low orhigh rotation speed, where low is preferably at least 10 rpm and e.g.not more than 2000 rpm. The composite product 40 and compounding of thematerials can be formed with any of these or combination of these andsome other process steps. Any of the mixers or extruders might containsome pre or post processing directly included in the extruder or mixeror by connecting shortly before or after the extruder. Advantageously,shredding, drying, and/or mixing are done in continuous process directlyconnected to extruder.

Forming of granulates, pellets or a similar composite product is usuallymade with granulation tool which is attached to an extruder or a meltpump. The granulating tool can be either a cold face cutter or a hotface cutter. One example of a suitable cold face cutter granulating toolis a strand pelletizer. In a hot face cutter, granulates are cut in meltform at the die plate. Suitable hot face cutter pelleting units can bedivided, for example, into three categories: cutting and cooling in theair, cutting and cooling in water or cutting in the air and cooling inwater.

Advantageously, the primary mixing stage is implemented with anextruder. In this case, after the primary mixing stage, the extruder ispreferably also used to form the composite product, for example pelletsor granulates.

Advantageously, the mixture 15 containing the organic natural fibermaterial 11, 11 a and the matrix material 12 is extruded. In oneembodiment, the mixture 15 is extruded after at least one pre-treatment.In one embodiment, the organic natural fiber material is supplied intothe extrusion directly after the crushing. In one embodiment, the matrixmaterial is mixed with the organic natural fiber material in connectionwith the extrusion without any pre-treatment stage.

In the case of the extrusion, any suitable single-screw extruder ortwin-screw extruder, such as a counter-rotating twin-screw extruder or aco-rotating twin-screw extruder, may be used. The twin-screw extrudercan have parallel or conical screw configuration. In one embodiment,different pelleting tools can be used in connection with the extruder.In one embodiment, the extrusion stage comprises a granulation step. Inone embodiment, the granulation step is arranged after the extrusion. Inone embodiment, the granulation step is a separate stage after theextrusion stage.

In an example, the melt of the mixture 15 comprising the organic naturalfiber material and the matrix material is conveyed to a co-rotatingparallel twin screw extruder, through melt pump to die plate to formstrand of the mixture. This is preferably granulated after cooling ofstrand. In one example, a co-rotating conical twin-screw extruder isused for the composite production. The screw volume can be, for example,from 4 to 8 times bigger at the beginning of the screw than in the endof the extruder.

In an advantageous example, an extruder is used to form the compositeproduct, for example, granulates. During the extrusion, the mixture 15comprising organic natural fiber material and the matrix material isextruded in the extrusion step and preferably granulated in thegranulation step. In the granulation, counterpressure is preferablyused.

One example of the extrusion is compounding with a co-rotating twinscrew extruder with strand pelletizing. In this case, materialcomponents are fed into main feed of the compounding extruder at thebeginning of the screws so melting can start as soon as possible.

One example of the extrusion is compounding with a conicalcounter-rotating twin screw extruder with underwater pelletizing tool.In this case, material components are fed into main feed of thecompounding extruder at the beginning of the screws so melting can startas soon as possible.

One example of the extrusion is compounded with a single screw extruderwith screening unit and water ring pelletizing tool. In this case,material components are fed into main feed of the extruder at thebeginning of the screws so melting can start as soon as possible.

The maximum conveying capacity of the extruder can be estimatedaccording to equation:V_(slip) ^(.)=nT A_(free)  Eq. (5)where n is rotation speed (1/s), T is pitch, and A_(free) is free crosssection area of the extruder.

Plastic melts adhere to the wall of barrel and thus the real conveyingvolume is less than in an ideal situation. The conveyed volume of suchmaterial for pressure-free conveying in multi-flighted profiles can beestimated according to equation:V_(est) ^(.)=0.5 nT A_(free)  Eq. (6)

The available volume or cross section area inside the screw of theparallel co-rotation twin screw extruder can be calculated based oninformation of machine supplier or literature. For double flighted screwdesign the free cross section area of such extruder can be calculatedaccording to equation:A_(free)=D_(a) ²x₂  Eq. (7)where D_(a) is outer diameter of screw, x₂ is coefficient of doubleflighted screw according to cross-section area diagram of R. Erdmenger.

If we estimate that the bulk density of fiber conveyed to the extruderis the same as the apparent bulk density, we can calculate thevolumetric flow of fiber to the machine according to equation:

$\begin{matrix}{{\overset{.}{V}}_{fibre} = \frac{{\overset{.}{m}}_{fibre}}{\rho_{apparent}}} & {{Eq}.\mspace{14mu}(8)}\end{matrix}$where m_(fiber) is mass flow of fiber and ρ_(apparent) is apparent bulkdensity of fibrous material.

When fiber is fed with maximum capacity to extruder, we can assume thatthe conveyed volume is similar to V_(slip) (eq. 5).

The invention may provide composite products with good mechanicalproperties. Advantageously, the composite product is a naturalfiber-polymer composite product. In one embodiment, a composite productcomprises wood based material and matrix material.

Theoretical/calculatory density (ρ_(t)) of a composite material may becalculated from the masses and the densities of each individualcomponent according to equation:

$\begin{matrix}{\rho_{t} = {\left( {m_{1} + m_{2} + \ldots + m_{n}} \right)/\left( {\frac{m_{1}}{\rho_{1}} + \frac{m_{2}}{\rho_{2}} + \ldots + \frac{m_{n}}{\rho_{n}}} \right)}} & {{Eq}.\mspace{14mu}(9)}\end{matrix}$where m₁, m₂, and m_(n) are the masses of each individual component ofthe composite material, e.g. the composite product or the mixturecontaining fiber material and matrix material, and ρ₁, ρ₂, ρ_(n) are thedensities of each individual component of the composite material, e.g.the composite product or the mixture containing fiber material andmatrix material.

Advantageously, the theoretical density of the mixture comprising orconsisting of fiber material and matrix material is between 930-1600kg/m³, preferably between 1000-1500 kg/m³. The theoretical densityvaries depending on components of the mixture and their densities.

Advantageously, the density of the composite product is between 0.90 and1.6 g/cm³, or between 0.93 and 1.5 g/cm³, more preferably between 0.95and 1.30 g/cm³, or between 0.97 and 1.20 g/cm³, and most preferablybetween 1.00 and 1.15 g/cm³.

Preferably, the density of the mixture is at least 85%, preferably over90%, more preferable 95% and most preferable over 98% of the theoreticaldensity. In an embodiment, the density of the mixture is at most 99.9%of the theoretical density of the theoretical density.

Preferably, the density of the composite product is at least 85%,preferably over 90%, more preferable 95% and most preferable over 98% ofthe theoretical density. In an embodiment, the density of the compositeproduct is at most 99.9% of the theoretical density of the theoreticaldensity.

Advantageously, the density of the composite product in a granulate formis between 0.90 and 1.30 g/cm³, more preferably between 0.95 and1.20g/cm³, and most preferably between 0.97 and 1.15 g/cm³.

Advantageously, the density of the composite product in a granulate formis between 0.90 and 1.10 g/cm³, more preferably between 0.95 and 1.10g/cm³, and most preferably between 0.97 and 1.08 g/cm³ if the amount ofthe organic natural fiber material in the granulate is less than 40 wt.%.

Advantageously, the density of the composite product in a granulate formis between 0.95 and 1.20 g/cm³, more preferably between 0.97 and 1.15g/cm³, and most preferably between 1.00 and 1.10 g/cm³ if the amount ofthe organic natural fiber material in the granulate is between 40 and 50wt. %.

Advantageously, the density of the composite product in a granulate formis between 0.95 and 1.30 g/cm³, more preferably between 1.00 and 1.20g/cm³, and most preferably between 1.03 and 1.15 g/cm³ if the amount ofthe organic natural fiber material in the granulate is at least 50 wt.%.

Formation of porosity into the composite product reduces the density ofsaid product. Ideally, there is no unwanted porosity in the compositeproduct. In practice, some porosity may exist no matter how good theprocess is in regard to minimizing the formation of porosity. Therefore,density can be used as one quantity for characterization of organicnatural fiber—thermoplastic polymer composite product. A compositeproduct can be characterized by its theoretical/calculatory density andits experimental density.

The term “pore volume” refers to a sum of partial volumes formed of gasvolumes inside the object compared with the total volume of the object.In one embodiment, the pore volume of the mixture and/or the compositeproduct is under 10%, preferably under 5%, more preferable under 2% andmost preferable under 1%.

Organic natural fiber material has the character that it absorbs water.The amount of water absorption depends on the condition around thematerial. Cellulose fibers absorb water quite rapidly, but when fibersare covered by hydrophobic matrix material, the absorption is muchslower. Absorption rate depends on the character of the matrix material,organic natural material content, but other things like additives canincrease or decrease the absorption rate.

Advantageously, a dry composite product 40, 40 a, 40 b absorbs moistureunder 1.5%, under 1.0%, or under 0.85%, more preferably under 0.7%,under 0.6% or under 0.5%, and most preferably under 0.4%, under 0.3%,under 0.2% or under 0.15% from the weight of the composite product inthe time of 48 hours (65% RH and 27° C. atmosphere).

The composite product 40, 40 a, 40 b may be in the form of granulates.In this case, preferably the sizes of the granulates are in the samerange. The weight of one granulate is preferably 0.01-0.10 g, and in oneembodiment more, and in one embodiment less. Preferably, the weight ofone granulate is 0.015-0.05 g. The weights of hundred granulates ispreferably between 1 and 10 g. Preferably, the weight of 100 granulatesis between 1.5 and 5 g. More preferable the weight of 100 granulates isbetween 2.0 and 4.0 g. Standard deviation is preferably under 15%, morepreferably under 7%, and most preferable under 2%.

In one embodiment, the organic natural fiber material (the amount beingbetween 5 and 95 wt. %, preferably between 10 and 60 wt. % or between 15and 40 wt. %) is mixed with polymer (the amount being between 5 and 95wt. %, preferably between 30 and 90 wt. % or between 40 and 80 wt. %)and additives (the amount being between 0 and 50 wt. %, preferablybetween 0 and 30 wt. % or between 5 and 20 wt. %) before adding themixture, for example, into the extruder.

The present invention provides an industrially applicable, simple andaffordable way of making intermediate composite products 40 a and finalcomposite products 40 b from the organic natural fiber material andmatrix material. The method according to the present invention is easyand simple to realize as a production process.

The method according to the present invention is suitable for use in themanufacture of different products from different organic natural fibermaterials.

Feeding of the main components, i.e. the matrix material and the organicnatural fiber material, may be more difficult, if the size of machinesused for the process is too small, even if the calculated bulk densityis low. In addition, very large sized machines may cause poorer mixingeffect or other disadvantage(s). Therefore, if an extruder is used,advantageously the diameter of the extruder screw in the feeding area isat least 30 mm, at least 40 mm, or at least 50 mm, more preferably atleast 60 mm or at least 70 mm, and the most preferably at least 90 mm orat least 110 mm. In addition or alternatively, the diameter of theextruder screw in the feeding area is preferably not more than 550 mm ornot more than 500 mm, more preferably not more than 450 mm or not morethan 400 mm, and most preferably not more than 350 mm or not more than300 mm. If a batch process is used instead of the extruder or anothercontinuous process, the free volume used is preferably at least 200liters, at least 400 liters or at least 500 liters, more preferably atleast 600 liters or at least 800 liters, and most preferably at least1000 liters or at least 1500 liters.

Advantageously the production capacity of the apparatus used for themanufacturing process is at least 300 kg/h or at least 400 kg/h, morepreferably at least 500 kg/h or at least 700 kg/h, and most preferablyat least 1000 kg/h or at least 1500 kg/h.

Thanks to the method according to the present invention, it is possibleto provide, among other things, homogeneous free-flowing granulates. Anadditional technical effect is to produce granulates for furtherprocessing. It is often important that good compounding is achievedbetween the organic natural fiber material and matrix material.

In one embodiment, the composite product is an intermediate product,such as pellets or granulates, which is preferably used in manufacturingof a final product. In another embodiment, the composite product of thepresent invention is a final product. The final product may bemanufactured from the intermediate composite product, e.g. granulates,by any suitable method, for example by injection moulding, film casting,blow moulding, rotomoulding, thermoforming, compression moulding,re-extrusion, profile extrusion, sheet extrusion, film extrusion, and/orfiber extrusion, or the like. In one embodiment, the granulates of thecomposite product are used in the forming of the final product. In oneembodiment, the granulates are finish-treated. Finish-treatment forgranulates comprises, for example, drying, dust removing, classificationand/or packing.

The composite product that is the final product, is preferably formed bythe method selected from the group consisting of injection moulding,extrusion, and their combinations. In one embodiment, the final productis formed by injection moulding. In one preferred embodiment of theinvention, the composite product is formed by extrusion. In oneembodiment, the composite product is formed by a combination ofextrusion and injection moulding.

The composite product comprises a mixture containing the organic naturalfiber material and the matrix material. Preferably, the amount of themixture in the composite product is at least 20 wt. % or at least 35 wt.%, more preferably at least 45 wt. % or at least 60 wt. % and mostpreferably at least 70 wt. % or at least 80 wt. % calculated of thetotal weight of the composite product. Preferably, the composite productconsists of said mixture. Preferably, amounts of organic natural fibermaterial and matrix material are adjusted in the mixing.

Advantageously, the composite product according to the present inventioncomprises between 10 and 80 wt. % or between 12 and 70 wt. % morepreferably between 14 and 60 wt. % or between 16 and 50 wt. %, and mostpreferably between 18 and 40 wt. % or between 20 and 30 wt. % organicnatural fiber material.

Advantageously, at least 50 wt. % or at least 70 wt. %, more preferablyat least 80 wt. % or at least 90 wt. % and most preferably at least 95wt. % of the natural organic fiber material in the composite productcomes from the mixture 15.

Advantageously, the composite product according to the present inventioncomprises matrix material between 5 and 95 wt. %, more preferablybetween 20 and 90 wt. % or between 30 and 85 wt. % and most preferablybetween 40 and 80 wt. %.

Advantageously, the composite product according to the present inventioncomprises additives and/or fillers, the total amount of said additivesand fillers being between 0 and 50 wt. %, more preferably between 0.5and 40 wt. % and most preferably between 1 and 30 wt. %.

In one embodiment of the invention, the composite product has lightcolor without coloring agents. Preferably, pigments and coloring agentsare not needed to be used in the composite product of the invention. Thelight color means that the natural fibers are not degraded remarkably.

Advantageously, the composite product has good dispersion. Dispersion isthe term that describes how well other components are mixed with thematrix material, preferably with the polymer matrix. Good dispersionmeans that all other components are evenly distributed into material andall solid components are separated from each other i.e. all particles orfibers are surrounded by matrix material.

Advantageously, the composite product 40 forms or is a part of

-   -   a decking,    -   a floor,    -   a wall panel,    -   a railing,    -   a bench, for example a park bench,    -   a dustbin,    -   a flower box,    -   a fence,    -   a landscaping timber,    -   a cladding,    -   a siding,    -   a window frame,    -   a door frame,    -   indoor furniture,    -   a construction,    -   an acoustic element,    -   a package,    -   a part of an electronic device,    -   an outdoor structure,    -   a part of a vehicle, such as an automobile,    -   a road stick for snow clearance,    -   a tool,    -   a toy,    -   a kitchen utensil,    -   cookwear,    -   white goods,    -   outdoor furniture,    -   a traffic sign,    -   sport equipment,    -   containers, pots, and/or dishes, and/or    -   a lamp post.

The method of the present invention offers a possibility to prepare theproducts from organic natural starting material cost-effectively andenergy-effectively.

EXAMPLES

The invention is described in more detail by the following examples.

Example 1

In this example, which is shown in FIG. 1, a composite product 40 isformed from organic natural fiber material 11, 11 a and polymer basedmatrix material 12. The organic natural fiber material is birch pulpbased material. Polymer based matrix material is polyethylene.

The organic natural fiber material is crushed 23 by a grinding methodselected from the group consisting of crushing-based grinding,attrition-based grinding, abrasion-based grinding, cutting-basedgrinding, blasting-based grinding, explosion-based grinding, wetgrinding, dry grinding, grinding under pressure and their combinationsin order to form organic natural fiber material. In one embodiment thefiber material is crushed 23 by crushing-based grinding. In oneembodiment the fiber material is crushed by cutting grinding.Preferably, the fiber material is crushed so that fibers are separatedand cut from the organic natural fiber material. In one embodiment thegrinding device used for grinding the fiber material is selected fromthe group consisting of impact mill, air jet mill, sand mill, bead mill,pearl mill, ball mill, vibration mill, screw mill and theircombinations. The grinding can be performed in one or more grindingsteps by one or more grinding methods. In one embodiment the fibermaterial is formed by grinding the fiber material in one or more steps.Preferably the organic natural fiber material 11, 11 a is crushed 23 bycutting grinding. The fibers of the organic natural fiber material areseparated in a separation stage 24 before the contacting step of theprimary mixing stage 36 to form bulky organic natural fiber materialcomposition 40. A compression ratio of the organic natural fibermaterial composition 40 in the contacting step of the mixing is 8 at themost.

The fibers of organic natural fiber material 11, 11 a are mixed withpolymer-based matrix material 12 in the primary mixing stage 36 withoutcompression to form a mixture 15. The polymer-based material 12 isarranged in the form of melt at least in the contacting step 36 a of theprimary mixing stage in which the organic natural fiber material comesin contact with the melt polymer-based material. The organic naturalfiber material is mixed lightly and in the presence of air with thepolymer-based material in the mixing step in order to form the mixtureso that the mixing is made without a compression and the organic naturalfiber material is evenly distributed to a mixing volume and the organicnatural fiber material become wet by the polymer-based material.

The intermediate composite product 40 a is formed from the mixture byextrusion. The intermediate 40 a composite product is in the form ofgranulates.

A final composite product 40 b is formed from the intermediate compositeproduct granulates, e.g. by an additional extrusion step.

Example 2

In this example, which is shown in FIG. 2, a composite product is formedfrom organic natural fiber material 11, 11 a and polymer based matrixmaterial 12. The organic natural fiber material is pine pulp basedmaterial. Polymer based matrix material is polyethylene.

The organic natural fiber material is crushed 23 to form bulky organicnatural fiber material 11 a and after the crushing 23 the organicnatural fiber material is fed into a heat mixing, i.e. into a mixingwhere temperature is increased, in which polymer-based matrix materialis added into the fiber material. The mixture 15 containing the organicnatural fiber material and polymer-based matrix material are fed in theextrusion stage in which the composite product 40 is formed.

Example 3

In this example, which is shown in FIG. 3, a composite product 40 isformed from a mixture 15 containing organic natural fiber material 11,11 a and polymer based matrix material 12 by an extrusion stage.

During the extrusion stage the mixture 15 is first extruded in anextrusion step 39 a and then granulated in a granulation step 39 b. Inthe granulation step counterpressure is used.

Example 4a

One example of extrusion is compounding with a parallel co-rotating twinscrew extruder with strand pelletizing. Material components are fed intoa main feed of compounding extruder at the beginning of the screws somelting can start as soon as possible.

Example 4b

One example of extrusion is compounding with a parallel co-rotating twinscrew extruder with an underwater pelletizing tool. Polymer-based matrixmaterial and additives are fed into a main feed of compounding extruderat the beginning of the screws so melting can start as soon as possible.The organic natural fiber material is fed to melt polymer from side feedof compounding extruder.

Example 5

One example of extrusion is compounding with a conical counter-rotatingtwin screw extruder with an underwater pelletizing tool. Materialcomponents are fed into a main feed of compounding extruder at thebeginning of the screws so melting can start as soon as possible.

Example 6

One example of extrusion is compounding with a single screw extruderwith a screening unit and a water ring pelletizing tool. Materialcomponents are fed into a main feed of extruder at the beginning of thescrews so melting can start as soon as possible.

Example 7

The maximum conveying capacity of an extruder can be estimated accordingto equation:V_(est) ^(.)=nT A_(free)  Eq. (5)where n is rotation speed (1/s), T is pitch and A_(free) is free crosssection area of extruder.

Plastic melts adhere to the wall of a barrel and thus the real conveyingvolume is less than in an ideal situation. The conveyed volume of suchmaterial for pressure-free conveying in multi-flighted profiles can beestimated according to equation:V_(est) ^(.)=0.5 nT A_(free)  Eq. (6)

The available volume or cross section area inside the screw of theparallel co-rotation twin screw extruder can be calculated based oninformation from machine supplier or literature. For a double flightedscrew design the free cross section area of such extruder can becalculated according to equation:A_(free)=D_(a) ²x₂  Eq. (7)where D_(a) is outer diameter of screw, x₂ is coefficient of doubleflighted screw according to cross-section area diagram of R. Erdmenger.

In the example this x₂ is 0.55, when D/d ration is 1.55 and outerdiameter of screws is 50 mm. For this machine the free cross sectionarea would be 0.138 dm² and available volume on the length of feedingzone 82 mm would be 0.11 liters.

Fiber material is fed 60 kg/h to the extruder and polypropylene melt 140kg/h while having extruder rotation speed of 350 rpm. This would mean0.57 kg/(h rpm) of throughput, and 0.17 kg/(h rpm) or 17 g/s or 2.9 g offiber feed per revolution of extruder screw. If we estimate that thebulk density of fiber conveyed to the extruder is the same as theapparent bulk density we can calculate the volumetric flow of fiber tothe machine according to equation:

$\begin{matrix}{{\overset{.}{V}}_{fibre} = \frac{{\overset{.}{m}}_{fibre}}{\rho_{apparent}}} & {{Eq}.\mspace{14mu}(8)}\end{matrix}$where m_(fiber) is mass flow of fiber and ρ_(apparent) is apparent bulkdensity of fibrous material. When we have an apparent bulk density of 68g/l (dry weight), we have 0.245 l/s fiber volumetric flow to extruder.

When fiber is fed with maximum capacity to the extruder, we can assumethat the conveyed volume is similar to V_(slip) (eq. 5) and thus,according to equation 5, with pitch (T) of 60 mm, we calculatevolumetric flow of 0.481 Vs, where we need to subtract the volume ofpolymer melt (0.103 Vs). When using polypropylene the melt density at200 C is 0.74 kg/dm³ and if the air volume of melt is similar to polymermelt, we can calculate “available volume” in the screw for the fiber.

Based on these we can get “the minimum calculated bulk density” at themoment when fiber is incorporated to polymer melt: 17 g/s/0.379liter/s=44 g/liter. When we know that the apparent bulk density is 68g/l, we have a compression coefficient of 0.65. By having thiscompression coefficient on that level until the fiber is wet, the fiberis well dispersed into the plastic with good mechanical properties andwith some degradation of polymer.

Example 8

The maximum conveying capacity of an extruder can be estimated accordingto equation 5. The available volume or cross section area inside thescrew of the parallel co-rotation twin screw extruder can be calculatedbased on information from machine supplier or literature. For doubleflighted screw design the free cross section area of such extruder canbe calculated according to equation 7.

In this example x₂ is 0.55, when D/d ration is 1.55 and outer diameterof screws is 50 mm. For this machine the free cross section area wouldbe 0.138 dm².

Fiber material is fed 60 kg/h to the extruder and polypropylene melt 140kg/h while having extruder rotation speed of 250 rpm. This would mean0.8 kg/(h rpm) of throughput, and 0.24 kg/(h rpm) or 17 g/s or 4 g offiber feed per revolution of extruder screw. If we estimate that thebulk density of fiber conveyed to the extruder is the same as theapparent bulk density we can calculate the volumetric flow of fiber tothe machine according to equation 8. When we have bulk density of 68 g/l(dry weight) we have 0.245 Vs fiber volumetric flow to the extruder.

When fiber is fed with maximum capacity to the extruder, we can assumethat the conveyed volume is similar to V_(slip) (eq. 5) and thus,according to equation 5, with pitch (T) of 60 mm, we calculatevolumetric flow of 0.344 Vs, where we need to subtract the volume ofaerated polymer melt (0.103 Vs). When using polypropylene the meltdensity at 200° C. is 0.74 kg/dm³ and if the air volume of melt issimilar to polymer melt, we can calculate “available volume” in thescrew for the fiber.

Based on these we can get “calculated bulk density” at the moment whenfiber is incorporated to polymer melt: 17 g/s/0.241 liter/s=84 g/liter.When we know that the apparent bulk density is 68 g/l, we have acompression coefficient of 1.02. By having this compression ratio onthat level until the fiber is wet, the fiber is well dispersed into theplastic with good mechanical properties and only slightly degradation ofpolymer.

Example 9

This example relates to a Z-blade mixer.

A composite material is prepared with a double-z-kneader. The kneader isa batch mixer with a volume of approximately 3 dm³. It has twocounter-rotating Z-blades, the mixing speed is constant and temperatureis controlled. Due to the low rotation speed of the mixing blades, lowshear forces and low heat generation by friction is expected. Thecomposite material was prepared as follows:

-   1. The kneader was heated to 190° C.,-   2. 300 g of HDPE polymer was melted in the mixer for 10 min,-   3. 17 g of coupling agents were added to the polymer melt to form    matrix material and mixed for 5 min,-   4. 210 g of oven dry organic natural fiber material, which is in the    form of birch cellulose flakes, where 80% of flakes have a thickness    between 1 micron and 20 micrometers and the apparent bulk density of    the material is 100 g/dm3, was added to the polymer melt,-   5. Mixing was continued until the compound appeared well mixed and    homogenous with good dispersion of the organic natural fiber    material in the matrix material and minimal thermal degradation of    the components, and-   6. the mixer was emptied and the prepared composite material was    cooled in air.

In this specific example the calculated bulk density of organic naturalfiber material is approximately 90 g/dm³, when the volume of the mixingelements, matrix material and additives are taken into account in theavailable free volume of the mixer. In this specific example thecompression ratio R is approximately 0.9.

Example 10

This example relates to a Z-blade mixer.

A composite material is prepared with a double-z-kneader. The kneader isa batch mixer with a volume of approximately 3 dm³. It has twocounter-rotating Z-blades, the mixing speed is constant and temperatureis controlled. Due to the low rotation speed of the mixing blades, lowshear forces and low heat generation by friction is expected. Thecomposite material was prepared as follows:

-   1. the kneader was heated to 190° C.,-   2. 180 g of polypropylene was melted in the mixer for 10 min,-   3. 11 g of coupling agents were added to the polymer melt to form    matrix material and mixed for 5 min,-   4. 169 g of organic natural fiber material, in the form of crushed    eucalyptus cellulose having moisture content of 7% and apparent bulk    density of 40 g/dm³ (dry weight) was added to the polymer melt,-   5. mixing was continued until the compound appeared well mixed and    homogenous with good dispersion of the organic natural fiber    material in the matrix material and minimal thermal degradation of    the components, and-   6. the mixer was emptied and the prepared composite material was    cooled in air.

In this specific example the calculated bulk density of organic naturalfiber material is approximately 70 g/dm³, when the volume of the mixingelements, matrix material and additives are taken into account in theavailable free volume of the mixer. In this specific example thecompression ratio R is approximately 1.7.

Example 11

This example relates to mixing without compression.

In this example organic natural fiber material and matrix materialcontaining polymer and additives are mixed with a batch type internalmixer without compression. In this embodiment the volume of the mixer is440 liters. 45 kg polypropylene, 3 kg additives and 12 kg organicnatural fiber material is mixed with this mixer. Moisture content of thefiber material is 3%. All ingredients are first fed into the mixer andthe mixer is started. Additional external heating is used, becausefriction is low and melting of the polymer takes too long.

Polypropylene is injection moulding grade polypropylene. Organic naturalfiber material is pulp based fibers from crushed paper sheets. Additivesare polypropylene based additives.

Density of the melted polypropylene is 0.74 kg/liter and volume of thepolypropylene in the mixer is 60.81 liters. Volume of the meltedadditives in the mixer is 4.05 kg/liter. Bulk density of the dry organicnatural fiber material is 0.05 kg/liter and volume of the dry organicnatural fiber material in the mixer is 12 kg*0.97/0.05 kg/liter=232.8liters. 3% moisture content vaporize during processing.

Free volume for the fiber material in the mixer 440−60.81−4.05=375.14liters Calculated density of the dry fibers in the mixer is 12kg*0.97/375.14 liters=0.031 kg/liter. In this embodiment the compressionratio R is 0.031 kg/liter/0.05 kg/liter=0.62 so mixing is made withoutany compression to the fibers.

Example 12

This example relates to mixing with a heating/cooling mixer.

In this example composite material is prepared with aheating/cooling-mixer. In this embodiment the volume of the heatingsection of the mixer is 800 liters and the volume of the cooling sectionof the mixer is 1700 liters. Heat is generated by friction with mixingelements. 180 kg organic natural fiber material and matrix materialcontaining 90 kg polypropylene and 30 kg additives are fed into theheating section of the mixer. Moisture content of the fibers is 5%.Moisture is vaporized during processing.

Polypropylene is injection moulding grade polypropylene. Additives aremineral fillers and polypropylene based stabilizers. Organic naturalfiber material is mechanically pre-processed eucalyptus chemical pulp.90% of the fiber material including possible agglomerates is under 2 mmlength.

All raw materials are first fed into the heating section of the mixerand the mixer is started. Mixing continues until the temperature is 220°C. and polymer is totally melted. The fiber material and additives arenow dispersed with polymer melt. Homogeneous composite material iscooled in the cooling section of the mixer until the temperature is 50°C. and material is totally solid. After cooling the mixer the materialis fluffy and color is light brown.

Density of melted polypropylene is 0.74 kg/liter on volume which is121.62 liters. Total volume of additives is 45 liters. Free volume forfibers is 800−121.62−45=633.38 liters. Bulk density of dry fibers is0.25 kg/liter. Calculated density of the dry fibers in the mixer is 180kg*0.95/633.38 liters=0.27 kg/liter. In this embodiment the compressionratio in the mixer is 0.27 kg/liter/0.25 kg/liter=1.08.

Example 13

In this example organic natural fiber material, polymer and additivesare mixed in a batch process with a so-called internal mixer. In thisembodiment the volume of the mixer is 5 liters. Organic natural fibermaterial is chemically and mechanically modified chemical pulp made ofbirch. The bulk density of fiber material is 109 g/l, at moisturecontent 6.5%.

2.35 kg polypropylene, 0.12 kg additives and 1.72 kg fiber material isadded to mixer. Fibers of the fiber material are incorporated to thepolymer when polymer is in melted form. Density of melted polypropyleneand additives together is 0.76 kg/liter and volume of the polypropyleneand additives in the mixer is 3.25 liters. Bulk density of the fibermaterial without moisture is 0.102 kg/liter.

Free volume for the fiber material in the mixer is 5 liter−3.25liter=1.75 liter and thus, the calculated bulk density is 1.61 kg/1.75liter=0.92 kg/liter, when the moisture content of the fiber material istaken into account. The compression ratio R is 0.92/0.102=9, so mixingis performed with high compression to the fibers. This makes theconditions unfavourable for good wetting of fibers, and thus, dispersionof fibers to matrix is poor.

Example 14

In this example organic natural fiber material, polymer and additivesare mixed with a continuous process. In this embodiment the rotationspeed of mixing elements is adjusted so that the volumetric flow of themixture is 0.95 liters/s. The melt of the mixture is conveyed to aco-rotating parallel twin screw extruder, through a melt pump to a dieplate to form a strand of the mixture. This is granulated after coolingof the strand.

Organic natural fiber material is chemically and mechanically modifiedchemical pulp made of conifer having a bulk density of fiber material125 g/l at moisture content 1.5%. The organic natural fiber material inthis example has a flake form meaning that the thickness of flakesvaries from 2 microns to 15 microns and the width is at least 2 timeslarger than the thickness.

250 kg/h polypropylene and additives is fed to the mixer as well as 200kg/h organic natural fiber material and 50 kg/h talc. Fibers of theorganic natural fiber material and talc are incorporated to the polymerwhen polymer is in melted form. Density of melted polypropylene andadditives together is 0.76 kg/liter and density of talc 2.75 kg/liter.Thus, the volumetric flow of the polypropylene, additives and talc inthe mixer is 0.097 liter/s. Bulk density of the organic natural fibermaterial without moisture is 0.123 kg/liter.

Free volume for the organic natural fiber material in the mixer is 0.95liter/s−0.097 liter/s=0.853 liter/s and thus, the calculated bulkdensity is 55.6 g/s/0.853 liter/s=65 g/liter, when moisture content ofthe fiber material is taken into account. The compression ratio R is 65g/liter/123 g/liter=0.53. This makes the conditions potential for goodwetting of fibers.

Example 15

In one example a co-rotating conical twin-screw extruder was used forthe composite production. This extruder has a huge feed volume, but thescrew volume can be ca. ⅛of that volume in the end of the screw. Whenthe fiber materials go through the screw, they are compressed and thepressure increase at same time. This can cause the bulk density to bequite high, when the organic natural fiber material touches the matrixmaterial in the melt form.

Polypropylene and pine cellulose based organic natural fiber materialare used in this example. The organic natural fiber material in thisexample has a flake form meaning that the thickness of flakes variesfrom 2 microns to 15 microns and the width is at least 2 times largerthan the thickness. The alfa-cellulose content of the material is below90%. The bulk density of the dry organic natural fiber material is 120g/liter. The free volume in the beginning of the screw is 1.6 liters.The through put was 500 kg/h and the natural fiber content was 50%. Thefeed volume of matrix material in the melt form was 0.094 liter/s, whenmelt density was 0.74 kg/l. The organic natural fiber material was fedat the same time (0.58 liter/s). The extruder can easily take thisorganic natural fiber material amount and calculated bulk density isbelow the apparent bulk density of the organic natural fiber material.The extruder rotation speed was adjusted so that conveying capacity inthe beginning of the mixing part of the screw was 0.844 l/s. In thisembodiment polymer starts to melt in the beginning of the 1st mixingsection. The calculated bulk density can be defined when mass flow oforganic natural fiber material in the beginning of the mixing part ofthe screw was 69.4 g/s and available, free conveying capacity for thatmaterial was 0.75 Vs. Thus, the calculated bulk density in that pointwas 93 g/l and the compression ratio R was 0.77. In the beginning of thescrew the conveying capacity was ca. 5 times higher.

Example 16

In one example a co-rotating conical twin-screw extruder was used forthe composite production. This extruder has a huge feed volume, but thescrew volume can be ca. ⅛of that volume in the end of the screw. Whenthe fiber materials go through the screw, they are compressed and thepressure increases at same time. This can cause the bulk density to bequite high, when the organic natural fiber material touches the matrixmaterial in the melt form.

Polypropylene and birch cellulose based organic natural fiber materialare used this example. The organic natural fiber material in thisexample has a flake form meaning that the thickness of flakes variesfrom 2 microns to 15 microns and the width is at least 2 times largerthan the thickness. The alfa-cellulose content of the material is above70%. The bulk density of the dry organic natural fiber material is 60g/liter. The free volume in the beginning of the screw is 1.6 liters.The trough put was 500 kg/h and the natural fiber content was 40%. Thefeed volume of matrix material in the melt form was 0.113 liter/s andthe organic natural fiber material was fed at the same time (0.93liter/s). The extruder can take this organic natural fiber materialamount and calculated bulk density is below the apparent bulk density ofthe organic natural fiber material. The extruder rotation speed wasadjusted so that conveying capacity in the beginning of the mixing partof the screw was 0.844 l/s. In this embodiment polymer starts to melt inthe beginning of the 1st mixing section. The calculated bulk density canbe defined when mass flow of organic natural fiber material in thebeginning of the mixing part of the screw was 55.6 g/s and available,free conveying capacity for that material was 0.73 Vs. Thus, thecalculated bulk density in that point was 76 g/l and compression ratio Rwas 1.27. In the beginning of the screw the conveying capacity was ca. 5times higher.

Example 17

Measurements Relating to the Organic Fiber Material

When the organic natural fiber material content of a composite materialis unknown, several analysis methods can be used for determination ofthe organic natural fiber material content of the composite material.Analysis methods suitable for determination of the organic natural fibermaterial content of an unknown composite material include, but are notlimited to physical, chemical, thermal, optical and microscopy analysistechniques. The organic natural fiber material content of an unknowncomposite material can be analyzed, for example, with thermogravimetric,calorimetric, spectroscopic, crystallographic, tomographic, andmicroscopic analysis, and by selectively dissolving the differentcomponents comprising the unknown composite material in order to resolvethe mass fraction of the organic natural fiber material comprising theunknown composite material. The organic natural fiber material contentof an unknown composite, provided that the matrix material isnon-bio-based material and that the other components comprising theunknown composite are known or can be resolved, can also be determinedby quantifying the bio-based content of the composite according tostandard ASTM-D6866 or with similar analysis methods that candifferentiate between bio-based and non-bio-based chemical elementsincluding, but not limited to, methods based on carbon dating, andcalculating the organic natural fiber material content according to themolar fraction of the chemical element of interest in the organicnatural fiber material. In addition, the organic natural fiber contentof an unknown composite can be determined, for example, by x-raydiffraction and x-ray computed tomography techniques. The organicnatural fiber material content of an unknown composite can be determinedby different combinations of analysis methods including, but not limitedto, methods described above.

In an example, a sample of a composite material comprising organicnatural fiber material and non-bio-based polymers, such as petroleumbased polyolefins, is analyzed for bio-based content according toASTM-D6866 and the organic natural fiber material content of thecomposite material is calculated according to the molar fraction ofcarbon in the organic natural fiber material.

In another example, a sample of a composite material comprising organicnatural fiber material is analyzed with x-ray computed tomography andthe content of the organic natural fiber material within the sample isdetermined.

Example 18

Organic Natural Fiber Material

Due to the hygroscopic character of organic natural fibers, the fiberstypically contain moisture. The moisture content of the fibers depends,for example, on the origin of the fibers, on the storing conditions ofthe fibers, e.g. relative humidity and temperature of the surroundingswhere the fibers are stored, and on the processing of the fibers.Typically, the presence of moisture cannot be fully excluded whileprocessing organic natural fibers, and in some cases excess moisture canbe harmful.

In the case of organic natural fiber and thermoplastic or other polymercomposites, the presence of moisture in processing can cause, forexample, deterioration of product properties such as mechanical strengthand visual appearance. Processing temperatures of organic naturalfiber-thermoplastic/polymer composites are typically above the boilingpoint of water due to the higher than 100° C. melting and/or glasstransition temperatures of thermoplastic/polymers.

In processing of organic natural fiber-thermoplastic/polymer compositesat temperatures above boiling point of water, the vaporization ofmoisture contained in the fibers can cause formation of porosity intothe product material. The porosity can appear, for example, in the formof gas bubbles or as voids between fiber surfaces and matrix polymer inthe composite product.

Another reason for formation of porosity can be inclusion of air orother surrounding gases during processing due to insufficient gasremoval in the process. Especially, feeding of reinforcement fibersbrings a large volume of gases to be removed in the process. Forexample, in preparation of organic natural fiber—thermoplastic/polymercomposites by compounding extrusion sufficient venting is necessary inorder to remove gaseous substances including water vapor, entrained airand other gases, and other volatile components.

Example 19

Bulk Density and Compression Ratio

In an example, if 11.1 g of organic natural fiber material that has thebulk density 80 g/l and the moisture content 10 wt. %, the weight of drymaterial is 10.0 g and the bulk density is 72 g/l. The bulk density canbe calculated as follows: the material is weighted into a pot (2 liter)and the organic fiber material is mixed with a mixer. In this case thefiber material can be evenly distributed over the whole volume and thecalculated bulk density would be 10 g/2 l=5 g/l and the compressionratio R is 5/72=0.069. On the other hand, if some other materials thanthe organic fiber material are added to the same pot, the weight andvolume of these materials will be subtracted. If there are 10 g of talc(density of talc 2.75 g/cm³) and 11.1 g of organic material (the bulkdensity is 80 g/l and the moisture content is 10 wt. %), the weight ofdry material is 10.0 g and the bulk density is 72 g/l. In this case thevolume of talc is 10 g/2.75 g/cm³=3.6 cm³. The free volume for thefibers is reduced to 1.996 liters and the calculated bulk density wouldbe 10 g/1.996 l=5.01 g/l, and the compression ratio R is 5.01/72=0.070.

Example 20

Bulk Density and Compression Ratio

In an example, the organic fiber material is mixed with an extruder sothat material is fed and conveyed 10 g/s (dry) into mixing zone whichtransports materials forward 2 dm³/s. In this case the fiber materialcan be evenly distributed over the whole volume and the calculatedapparent bulk density would be 10 g/2 l=5 g/l. On the other hand, ifsome other materials than the organic fiber material are added to thesame volume, which is available at given time, the weight and volume ofthese materials will be subtracted. For example, for 10 g of organicfiber material (dry) and 10 g of talc (density of talc 2.75 g/cm³), thevolume of talc is 10 g/2.75 g/cm³=3.6 cm³. The free volume for thefibers is reduced to 1.996 liters and the calculated bulk density wouldbe 10 g/1.996 l=5.01 g/l.

Example 21

Bulk Density and Compression Ratio

In an example, in order to measure the bulk density value, the organicnatural fiber material is first mixed with a mixer (e.g. PhilipsHR1570/30) for a suitable time, such as 5 minutes, in a large bowl.During the mixing all compressed fibers and crushed particles areseparated. Then the weight and volume of this bulky fiber materialsample is carefully measured. The bulk density p is calculated bydividing the weight of this bulky organic fiber material by its volume.Because organic natural fiber materials can absorb quite a high amountof moisture, in all cases the content of water will be subtracted fromthe bulk density results and the results will be given for the drymaterials, e.g. the measured bulk density of organic natural fibermaterial is 100 g/l and moisture content is 5 wt. %. The bulk density ofthat material is 95 g/l. So the moisture content and the bulk densityare measured separately and the bulk density (dry) is calculated fromthe values.

Example 22

Calculated Bulk Density in the Extruder

Calculated bulk density in the extruder can be quite high and thecompression ratio over 1, if a high production capacity and high organicnatural fiber content is looked for. In this case the free volume isvolume inside the barrel, where the volume of the screw, matrix materialvolume and matrix material melt volume is reduced. When mixing takesplace in a short length of the screw or the conveying volume of thescrew is small compared to fiber material mass forced inside theextruder, the calculated bulk density can be quite high. If organicnatural fiber is fed 26.7 g/s and free conveying volume for fibre isonly 0.083 l/s, the calculated bulk density would be ca. 320 g/l andcompression ratio 4.7 with material having apparent bulk density of 68g/l.

It is possible to increase the volumetric conveying capacity by forcingthe organic fiber material to move faster than the screw and thus, it ispossible to decrease the calculated bulk density ρ_(calculated). Or, theorganic fiber material can be forced to counter flow so that thecalculated free volume is increased by spreading the organic fibermaterial to a longer distance, further inside the barrel. This can bedone by e.g. air. The compressed gas can be blown inside the barrel andthis gas can carry fibers further from the addition point. Also vacuumin the other point of barrel can cause the pressure difference totransport the fibers. In both cases the length where the mixing takesplace is longer and this reduces the calculated bulk density.

Example 23

Bulk Density

In this example, a sample of organic natural fiber material is collectedfrom a process flow, that can be considered to be well mixed and aeratedand where fiber agglomerates are disintegrated and for which additionalmixing, for example, by blenders, food mixers, concrete-mixers, andfluidization techniques is not required for determination of the bulkdensity, into a container of known volume and weight and the bulkdensity of the organic natural fiber material is obtained as the mass ofthe sample per unit volume.

Example 24

In this example, a sample from a process flow at a production line of acomposite mixture, wherein one component of the composite mixture isorganic natural fiber material, is collected and the organic naturalfiber material is separated by different separation and classificationmethods including, but not limited to, screening, cyclone separators,and vacuum separators. Bulk density of the separated organic naturalfiber material can be determined as described above.

Example 25

In one embodiment the composite product includes the organic naturalfiber material 40-60%, and dry composite product absorbs moisture under1.5% from the weight of the composite product in the time of 30 hours(50% RH and 22 ° C. atmosphere). In one embodiment the composite productincludes the organic natural fiber material 20-40%, and dry compositeproduct absorbs moisture under 1.3% from the weight of the compositeproduct in the time 30 hours (50% RH and 22° C. atmosphere). In oneembodiment moisture uptake from the atmosphere can be measured from thedry composite products. Before the measurement the composite productshave to be dried. Composite product should be dried at a temperature of120° C. for 48 hours before the measurement. For the moisture uptakemeasurement at least 10 grams of products will be placed on the plate.There should be only one granulate layer on the plate. Moisture uptakewill then be measured as a weight increase compared to the weight of dryproducts. So if the weight of dry composite product increases from 10.0g to 10.1 g, the result will be 1.0%. In these measurements theconditions are: temperature 22° C. and moisture content of air 50% RH.Different measurement times can be used depending on the need.

Example 26

In one embodiment the composite product includes the organic naturalfiber material 40%, and dry composite product absorbs moisture under0.7% from the weight of the composite product in the time of 4 days (50%RH and 23° C. atmosphere). In one embodiment the composite productincludes the organic natural fiber material 40%, and dry compositeproduct absorbs moisture under 0.6% from the weight of the compositeproduct in the time of 48 hours (50% RH and 23 ° C. atmosphere). In oneembodiment the composite product includes the organic natural fibermaterial 40%, and dry composite product absorbs moisture under 0.15%from the weight of the composite product in one hour (50% RH and 23° C.atmosphere). In one embodiment moisture uptake from the atmosphere canbe measured from the dry composite products. Before the measurement thecomposite products have to be dried. The composite product should bedried at a temperature of 120° C. for 48 hours before the measurement.For the moisture uptake measurement at least 30 grams of products willbe placed in the 2 dl cup. Moisture uptake will then be measured as aweight increase compared to the weight of dry products. So if the weightof dry composite product increases from 10.0 g to 10.1 g, the resultwill be 1.0%. In these measurements the conditions are: temperature 23°C. and moisture content of air 50% RH. Different measurement times canbe used depending on the need.

Example 27

In one embodiment the composite product includes the organic naturalfiber material 40%, and dry composite product absorbs moisture under0.85% from the weight of the composite product in the time of 4 days(65% RH and 27° C. atmosphere). In one embodiment the composite productincludes the organic natural fiber material 40%, and dry compositeproduct absorbs moisture under 0.7% from the weight of the compositeproduct in the time of 48 hours (65% RH and 27° C. atmosphere). In oneembodiment moisture uptake from the atmosphere can be measured from thedry composite products. Before the measurement the composite productshave to be dried. Composite product should be dried at a temperature of120° C. for 48 hours before the measurement. For the moisture uptakemeasurement at least 30 grams of products will be placed in the 2 dlcup. Moisture uptake will then be measured as a weight increase comparedto the weight of dry products. So if the weight of dry composite productincreases from 10.0 g to 10.1 g, the result will be 1.0%. In thesemeasurements the conditions are: temperature 27° C. and moisture contentof air 65% RH. Different measurement times can be used depending on theneed.

One skilled in the art readily understands that the differentembodiments of the invention may have applications in environments whereoptimization of the composite product is desired. It is also obviousthat the present invention is not limited solely to the above-presentedembodiments, but it can be modified within the scope of the appendedclaims.

The invention claimed is:
 1. A method for manufacturing a compositeproduct comprising organic natural fiber material and matrix material,wherein the organic natural fiber material has a lignin content of lessthan 1 wt. %, and wherein the method comprises: mixing the organicnatural fiber material with the matrix material in a primary mixingstage to form a mixture, the primary mixing stage comprising acontacting step in which the calculated bulk density of the organicnatural fiber material before the contacting step is under 300 kg/m³,the calculated bulk density referring to the bulk density of the organicfiber material comprising compressed and decompressed bulk densities,and being determined according to the equation${\rho_{calculated} = \frac{{mass}\mspace{14mu}{flow}\mspace{14mu}{of}\mspace{14mu}{fibre}}{{conveying}\mspace{14mu}{volumetric}\mspace{14mu}{flow}\mspace{14mu}{of}\mspace{14mu}{mixer}}},$the organic natural fiber material comes in contact with the matrixmaterial that is at least partly in a form of melt, and compressionratio of the organic natural fiber material is less than 4, whereincompression ratio is determined according to the equation$R = \frac{\rho_{calculated}}{\rho}$  wherein R is compression ratio,ρ_(calculated) is calculated bulk density of the organic natural fibermaterial, and ρ is apparent bulk density of the organic natural fibermaterial, the apparent bulk density referring to the bulk density of theorganic natural fiber material neither compressed nor decompressed, andbeing determined by dividing the weight of a sample of the organicnatural fiber material by its volume according to ISO 697, the methodfurther comprising: crushing the organic natural fiber material beforethe contacting step to form bulky organic natural fiber material whereinthe organic natural fiber material is at least partly in the form offlakes having a thickness of 1 to 30 micrometers and a width that is atleast 2 times the thickness after the crushing and forming a compositeproduct comprising the mixture.
 2. The method according to claim 1,wherein the pressure compressing the organic natural fiber material inthe contacting step is less than 1 bar.
 3. The method according to claim1, wherein the materials are mixed in a vacuum or in the presence ofnitrogen, air and/or helium.
 4. The method according to claim 1, whereinmoisture content of the organic natural fiber material is below 7% inthe contacting step of the mixing.
 5. The method according to claim 1,wherein the content of the organic natural fiber material is at least 20dry wt. % and 80 dry wt. % at the most calculated from the total dryweight of the composite product.
 6. The method according to claim 1,wherein the amount of fibers in flake form is at least 30 dry wt. %calculated from the total amount of the organic natural fiber material.7. The method according to claim 1, wherein the melting point of thematrix material is under 250° C. and/or the glass transition temperatureof the matrix material is under 250° C.
 8. The method according to claim1, wherein the composite product is formed by an injection moulding,and/or an extrusion.
 9. The method according to claim 1, wherein thematrix material is thermoplastic.
 10. The method according to claim 1,wherein a length of at least 90 wt. % of the organic natural fibermaterial is between 0.1 mm and 3 mm.
 11. A composite product obtainableby the process defined in claim
 1. 12. The composite product accordingto claim 11, wherein the composite product is in the form of granulates.13. The composite product according to claim 12, wherein the weight of100 granulates is between 2.0 and 4.0 g and standard deviation is under15%.
 14. The composite product according to claim 11, wherein thecomposite product that is dry absorbs moisture under 1.5% from theweight of the composite product in the time of 48 hours and at 65%relative humidity and a temperature of 27° C. and at atmosphericpressure.
 15. The method according to claim 1, wherein the compositeproduct is a granulated composite product, and the method furthercomprises forming a final composite product from the granulatedcomposite product, wherein the forming comprises injection molding, filmcasting, blow molding, rotomolding, thermoforming, compression molding,re-extrusion, profile extrusion, sheet extrusion, film extrusion, orfiber extrusion.